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Fraanje (1999) Use of Wood in new Dutch one family Dwellings since 1969


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hout, nieuwbouw, Nederland, houtgebruik Universiteit van Amsterdam PhD Fraanje PJ

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Fraanje (1999) Use of Wood in new Dutch one family Dwellings since 1969

  1. 1. Originalarbeiten á Originals Holz als Roh- und Werkstoff 57 (1999) 407±417 Ó Springer-Verlag 1999Use of wood in new Dutch one family dwellings since 1969 P. J. Fraanje 407The application of wood for building purposes, especially È È Holzverwendung fur neue hollandischewhen used in constructions, can be seen as a high quality È Einfamilienhauser seit 1969application. As wood is, in contrast with most other Die Verwendung des Rohstoffs Holz im Bauwesen, vor al-building materials, a renewable resource, and because the È lem fur Holzkonstruktionen, kann man als Nutzung vonenvironmental impact is relatively low, wood is promoted È hoher Qualitat ansehen. Holz ist im Gegensatz zu denby the Dutch government in the ``20% more wood for the meisten anderen Baumaterialien ein erneuerbarer Rohstoff.building sector programme. In this article an overview is Weil die Belastung der Umwelt relativ niedrig ist, wird diegiven of wood utilization in new one family dwellings È Holzverwendung durch die niederlandische Regierung im(OFDs), built in the past three decades. The wood use per Rahmen des Programms ,,20% mehr Holz im Bau`` gefor- Èaverage OFD dropped from 6.2 m3 in 1969 to 3.4 m3 in È dert. In diesem Beitrag wird die Holzverwendung fur neue1996. Most of the wood is currently applied to roof and È Einfamilienhauser (EFH) in den letzten dreiûig Jahrenwindow frames. It appears that there is a decrease in the analysiert. Fur ein EFH brauchte man im Jahre 1969 6,2 m3 Ètotal wood use for new OFDs and that the amount of wood Holz, 1996 dagegen nur 3,4 m3. Heute sind Dach undproducts per average OFD also shows a declining ten- È Fenster die wichtigsten Bauteile fur die Holzverwendung.dency, counterbalanced however by a growing gross ¯oor Es zeigt sich, daû sowohl die gesamte Holzverwendung alsarea and an increasing number of unsubsidized OFDs. For auch die durchschnittliche pro EFH laufend sinkt, obwohl1996, a balance of the total amount of wood applied in all È die Brutto-Boden¯ache der EFH gestiegen ist. Dies liegtOFDs with the input and output of wood products is daran, daû der Anteil nicht subventionierter EFH in denpresented. The total wood stock in all OFDs is estimated È letzten Jahren zunahm. Fur 1996 wird hier eine Bilanz derto amount 21 ´ 106 tonnes for 1996. This can be seen as a È gesamten Holzmenge fur alle EFH zusammen mit In- undreservoir out of which wood becomes available every year È Output von Holzprodukten prasentiert. Die gesamtethrough renovation and demolition of OFDs. This sec- Holzmenge in EFH betragt rund 21 ´ 106 t und steht jedes Èondary wood (together with wood waste from newly built È Jahr fur Abbruch und Renovierung von EFH bereit. DasOFDs) can be cascaded, so that the resource wood is È Altholz kann (zusammen mit Holzabfallen von Neubauten)optimally used. The article concludes with options to in- wieder verwendet werden (cascade), so daû der Rohstoffcrease the amount of wood used in new OFDs, by ± È Holz optimal genutzt wird. Eine Moglichkeit zur Steigerungamongst others ± increasing the market shares of timber È È der Holzverwendung fur EFH bietet z.B. die Erhohung desframe dwellings, wooden ¯ooring and wooden foundation È È Marktanteils im Holzskelettbau, bei holzernen Fuûbodenpiles. und Fundamentierungspfahlen.È 1 Introduction The use of timber in dwellings is interesting from an en- vironmental point of view, as wood is, in contrast to mostP.J. Fraanje other building materials, a renewable resource with rela-IVAM Environmental Research tively low environmental impact and a positive effect onUniversity of Amsterdam the indoor environment (Schneider 1986; Fraanje et al.P.O. Box 18180, 1990; La¯eur and Fraanje 1997). The utilization of the1001 ZB Amsterdam, The Netherlands resource of wood in the building sector, especially whenI thank Prof. Dr. L. Reijnders of the Interfaculty Department of used for structural purposes, can be seen as a high qualityEnvironmental Sciences (IDES) of the University of Amsterdam application and therefore is a good start for a cascadingfor his comments. I am grateful to Mr. W.J. de Graaf of PRC strategy (Fraanje 1997; La¯eur and Fraanje 1997). InBouwcentrum in Bodegraven, Mr. F.G.M. van Swam and Mr. general, the use of wood as a building material is envi- ÈR.G.A. Bult of Hugli Pollock Read in Utrecht, Mr. A.G. Oskam of ronmentally preferable to application in products with aDamen Consultants in Rotterdam (now working at Centre for shorter life time e.g. pallets, as carbon locked up in wood isSustainable Building in Utrecht) and Mr. E. Knapper of theNetherlands Central Bureau of Statistics (CBS), for supplying stored for a longer period of time (Fraanje and La¯eurdata. The research for this article was ®nancially sponsored by the 1994; Fraanje 1997; Drunen 1997).NWO-research programme for sustainability and environmental Against this background, the Dutch Ministry of Hous-quality. ing, Physical Planning and Environment (VROM) pub-
  2. 2. lished a report within the framework of its programme for working in renovation projects. Although being quantita- sustainable building in which an effort to increase the tively less important, this article is limited to newly built application of timber and other wood products in the dwellings. Speci®c data on wood use for renovation of building sector by 20% is formulated (Boonekamp 1995). dwellings are not available as most of the renovation Some important institutions in the building and civil en- activities are not recorded. gineering market, like the Ministry of Public Works and Apart from the new OFDs yearly some 20±30% of all Water Management as well as two umbrella organisations dwellings are new apartments in multi storey blocks. The of housing corporations, have committed themselves to amount of wood products per apartment constitutes a this goal. In 1990, the year of reference of the 20% more fraction of the wood products used for OFDs; in apart- wood programme, 2,150,000 m3 of wood products were ments built after 1968, 2.5 times less wood is applied than used in the whole Dutch building sector (residential, non in an OFD (de Graaf 1996). Therefore, within the section of408 residential and civil engineering) (Boonekamp 1995). For new dwellings only newly built one family houses (without 1990, the use of sawn wood and sheet material was esti- sheds) (OFDs) are taken into account. mated at an average of 2.8 m3 wood product per new dwelling, totalling 280,000 m3 net and 400,000 m3 gross 3 (excluding wooden foundation piles) for 97,500 new The use of wood in dwellings dwellings built in this year (Boonekamp 1995). In 1980, thebuilt between 1969 and 1982 average still was 3.8 m3 wood product per new dwelling There are unfortunately no detailed data covering the use (Fraanje et al. 1990). of wood in Dutch new OFDs during the 20th century. Within the framework of the 20% more wood pro- Estimates for the 1900±1945 period suggest that roughly gramme, the total amount of wood for the new dwellings 10.4 m3 of timber was applied in new OFDs (Botman has to be enlarged by about 100,000 m3 in the year 2000 1979), whereas only about 8.5 m3 were used in the 1945± (Boonekamp 1995). The object in view is to double the 1970 period (Botman 1979). It should be noted that earlier number of timber frame dwellings and to expand the mentioned estimates refer to analyses of typical single number of wooden carrying inner cavity walls, sloping OFDs; they are not a result of a representative cross-sec- roofs, wooden foundation piles and sheds (Boonekamp tion. Detailed data are available as to OFDs built between 1995). 1969 and 1982. In this paragraph, the application of wood Exact data on wood applications in new dwellings since products in new one-family dwellings in the period be- 1982 in the Netherlands are not available, but experts havetween 1969 and 1982 is analyzed. In the period between the impression that timber products lost ground in the 1969 and 1982, the Ministry of Housing and Physical residential sector (Eisma 1979) (Boonekamp 1995). Wood Planning (VRO) documented the use of building materials products seem to be more and more replaced by other in new dwellings, in the Quantitative Material Documen- materials like concrete and plastics, so the actual trend of tation (QMD). For a period of fourteen years, a unique wood utilization in the building sector tends towards the documentation was developed, however published only opposite direction of the ``20% more wood programme. partly and at different places (CBS 1976±1984; Eisma 1973± In an effort to trace the actual development of wood use1980 and van derWerff 1980±1985). In 1983, the Dutch and to view this against the background of longer term government decided to stop this documentation, due to trends, it is attempted to determine the average amount of cuts in expenditure. Since then some consultants have wood in new one family dwellings (OFD) in the Nether- emerged offering information per building product or lands over the last three decades. OFDs in the Netherlandselement for a commercial price, but no overview is given, built in this period typically have two ¯oors and an attic.and data are hardly published anymore. The attention is focused on which building elements are For the QMD, the utilized building material according usually made of wood and changes therein. Further, the to 1000±1200 plans for new dwellings was recorded. This total amount of wood in all OFDs in the Netherlands is represented a 1% cross-section of all new dwellings. Such estimated and a wood balance for 1996 is presented. Data recording was possible, as for all new houses authorization on the total wood stock and wood ¯ows are relevant for of the central government on the basis of drawings and determining the cascading potential of timber in the Dutch speci®cations was necessary. It should be noted that as OFD stock. Finally, some options for an increase in wood plans for building were used, the data for 1969 are rep- utilization for OFDs are given. resentative for the dwellings built in 1970, etc. A slight drawback of this method may be that minor differences 2 between plans and the actual dwellings are possible, New one family dwellings especially where ®nishing materials are concerned. Most of the timber used annually in the Netherlands is Based on the primary data of the Quantitative Material applied in the residential sector (NEI 1983; NEHEM 1983; Documentation, Table 1 lists the use of wood in different Fraanje and La¯eur 1994; Boonekamp 1995). Apart from construction elements and building products for one the 400,000 m3 for new dwellings, also about 650,000 m3 family dwellings without shed for the period 1969±1982. (gross) of wood and sheet material (boards, plywood etc) The table is divided into the categories foundation, ¯oor, was used for renovating dwellings in 1990 (Boonekamp facade, ceiling, wall, roof, door and staircase. Not included 1995). Wood is a light weight, strong, ¯exible, easy in the QMD are skirtings, roof laths, thresholds and indoor adaptable and workable (on the building site) building ®nishings, as well as timber used for shuttering and scaf- material which explains its popularity amongst contractors folding. Also excluded from the QMD is the use of wood
  3. 3. Table 1. The use of timber and boarding material in different construction elements and building products are given for one family dwellings without shed for the period 1969±1982 È ÈTabelle 1. Die Verwendung von Schnittholz und Brettmaterial in verschiedenen Konstruktionselementen und Baustoffen fur Einfamilienhauser ohne Schuppen in den Niederlandenvon 1969±1982Wood use in new one family dwellings (OFDs) without shed 1969±1982Number of OFDs 85100 91300 98500 112400 109900 100600 88600 93900 84500 81900 73300 68900 78375 63950 Building element year 69 70 71 72 73 74 75 76 77 78 79 80 81 82Foundation pieces 346800 366400 386300 370600 326600 326500 283600 316100 284000 131200 135000 140800 90700 73400 Wooden foundation pilesFloor Floor beams m3 39600 42600 33473 42311 36107 27145 19605 27188 22431 19162 16641 12513 7949 7642 Wooden ¯ooring 1000 m2 1484 1858 1936 2062 1482 808 610 687 464 392 331 274 121 111 Plywood 1000 m2 28 8 17 58 105 48 124 95 151 117 193 Chipboard 1000 m2 14 77 115 138 105 170 200 85 66 44 42 37 Planks of hardwood 1000 m2 31 5 10 4 16 0 0 22 0 0 0 0 0 0 Parquet 1000 m2 0 0 16 12 13 16 20 16 16 11 14 4 3 0Facade Wooden facade 1000 m2 11 1 8 23 nb 11 13 15 0 15 21 40 24 20 Wooden sheatings OFDs 4400 4400 5900 5600 6300 6900 6300 3700 2800 2000 1700 1000 Coniferous window frames 1000 m2 2712 2790 2746 2958 2641 2123 1478 1178 757 670 751 626 625 435 Hardwood window frames 1000 m2 382 422 730 1126 1332 1277 1433 1949 2033 1819 1269 1157 1238 1020 Parapets wood 1000 m2 138 133 189 342 422 460 364 441 448 399 288 187 173 174 Parapets plywood 1000 m2 28 31 46 72 79 70 73 65 63 62 38 51 49 Parapets ®breboard 1000 m2 2 2 5 2 0 1 1 0 0 0 0 0 0 Wooden parapet for balconies 1000 m2 28 42 25 31 14 24 33 30 29 46 16 28 20 9Ceiling Fibreboard ceiling 1000 m2 1467 1546 1606 1306 783 391 264 156 93 12 46 7 1 0 Wooden ceiling 1000 m2 234 250 219 356 759 641 535 605 687 289 211 204 103 55 Chipboard ceiling 1000 m2 nb nb 85 67 71 137 77 100 66 35 17 4 10 10Wall Wooden carrying inner cavity wall 1000 m2 nb 108 90 99 101 221 Non carrying interior wall chipboard 1000 m2 8 13 nb 425 465 374 328 260 197 130 105 112 120 66Roof Beams for roo®ng m3 80800 86900 82324 100482 102876 86139 76077 96266 88838 79523 61608 57123 53053 37893 Boarding spruce 1000 m2 3371 3215 2303 1880 1410 852 400 258 258 155 118 46 9 8 Boarding plywood 1000 m2 21 7 13 83 112 121 69 211 190 189 304 429 521 528 Boarding woodwool(cement) 1000 m2 239 69 174 156 260 120 60 48 35 45 22 0 1 3 Boarding chipboard* 1000 m2 137 65 119 83 278 6086 4839 4681 4435 3003 Reed ¯ax straw boarding 1000 m2 2324 3278 3648 5598 5993 5782 5485 6850 6217 included in chipboard data Roo®nsulation woodwool 1000 m2 119 76 142 136 63 78 18 0 62 0 0 0 0 0 (Ply)wood for gutters m3 1310 1260 1389 1618 1837 1820 1719 2190 2055 2156 1668 1157 713 575 Wooden dormer pieces 11440 10313 14300 12000 12900 10400 13840 15440 14160 17600 16800 12051 11092 8514 Wooden pivotal window pieces 5170 13630 20680 28012 24252 30174 32430 40138 29422 35881 43150 44556 61100 54219Doors Front door coniferous pieces 29500 30400 30000 31300 20000 20900 14000 12700 6100 5700 6800 4400 5300 3900 Front door hardwood pieces 40100 37800 46500 52500 59500 50300 48900 58900 59100 64800 54900 48900 53100 44100 Front door plywood pieces 14300 22000 20600 23600 22000 17900 13500 13800 8600 24200 20500 8200 10900 6900 Kitchen, terrace, balconydoor pieces 129000 131000 139700 164500 169100 157000 137600 160700 148100 141000 108400 93200 91700 70700 Outer doors (total) pieces 212900 221200 236800 271900 270600 246100 214000 246100 221900 222900 181700 154700 161000 125600 409
  4. 4. for constructions of inner walls and ceilings. Table 1 582 11100 52200 54358 shows dramatic decrease in wooden foundation piles, ¯oor beams, wooden ¯ooring and spruce boarding of roofs. Especially for window frames, inner door frames and front 743 13600 68000 66619 doors, hardwood gained market shares at the cost of co- niferous wood in the period 1969±1982. 663 4 19600 57600 58565 Estimation of the wood use in one-family dwellings (OFDs) in 1996 For the period after 1982, hardly any detailed information 729 22830 59800 62305410 on wood use in new dwellings is available. There are, however, reports with estimates of wood product market shares (Dielen 1985; de Graaf 1988; Boonekamp 1995; de 822 37410 66200 69615 Graaf 1996). For 1996, there are also informations available È from BuildsightÒ (produced by Hugli Pollock Read, Ut- recht 1997), a software programme for producers in the 847 29000 68500 71825 building market. Buildsight is based on about 1400 inter- views on building sites in combination with statistical information on total areas of roofs, walls etc. of newly 953 36200 74400 79815 built OFDs. As the interviews take place on the building sites, the data gathered are representative for the same year, so in contrast to the QMD, the data for 1996 refer to 904 30600 73500 76000 the OFDs built in 1996. In the following the wood use for 1996 in new OFDs is estimated. In 1996, 61,007 OFDs were realized, of which 1033 41300 86900 83200 36% were detached, while the other 64% of OFDs were built in a row (Buildsight 1997). Table 2 summarizes the wood use in new OFDs in 1996. These elements are the 1158 59700 90200 92800 Table 2. The estimated amount of wood products (in m3) ap- 1230 67800 99300 91100 plied in one family dwellings (without shed) built in 1996 Tabelle 2. Geschatzte Menge an Holzprodukten (m3) in Einfa- È È milienhausern (ohne Schuppen), die 1996 gebaut wurden 1129 67200 93100 81048 Building element m3 (1996) Foundation Wood use in new one family dwellings (OFDs) without shed 1969±1982 1082 71600 80993 76158 Wooden foundation piles 5630 * documentation modi®ed in 1978 (accounts for a sudden increase) Floor Floorbeams 7240 Plywood/OSB ¯ooring 4935 1016 72200 78204 67905 Facade Wooden facade 2800 Coniferous window frames (spruce, pine) 2310 1000 pieces Hardwood window frames 19940 Ceiling no estimation OFDs Wall pieces pieces Carrying inner cavity wall 2860 Roof Beams for roo®ng 58230 Boarding plywood/chipboard/OSB 66175 ** after 1975 data are extrapolated Plywood for gutters 1095 Wooden staircase to ®rst ¯oor Wooden dormers 1315 Wooden staircase to attic** Wooden inner door frames Wooden pivotal windowÃ) 2865 Doors Wooden outer doors 5320 Inner doors of wood 5490 Wooden inner door frames 2040 Table 1. (cont.) Staircases Wooden staircase to the ®rst ¯oor 9900 Staircases Inner doors Wooden staircase to the attic 6000 Total 204.145 * wood for window frames of dormers
  5. 5. same as the ones covered by the QMD (Table 1), with the hardwood to coniferous wood was about 90:10 in 1990 butexception of parapets. In order to outline the underlying changed to 85:15 in 1993 (Boonekamp 1994). Probably,data and assumptions for 1996, the speci®c building ele- this has to do with campaigns against the use of tropicalments of OFDs built in 1996 in which wood is applied are hardwood in combination with the emergence of techni-reviewed: cally well-constructed coniferous window frames.4.1 4.4Foundation CeilingMost wooden foundation piles are made of spruce (about Wood does not play a role anymore in this building element75%), the other 25% are larch and douglas (de Graaf 1988). except as a construction for ®xing gypsum board. ThisAccording to (Beukema 1997) 1±5% of all dwellings built in application was not recorded in the QMD. For all 110,000 4111995 by housing corporations is built on wooden piles. dwellings in 1987 de Graaf (1988) estimated a total wood useAnother estimate for 1996 arrives at 1% (Swam 1997). In of over 8,000 m3, mainly used in about 5,500 timber framethis article, the assumption is made that the market share of houses. For 1996, no data are available, and in accordancewooden piles amounts 2% of all OFDs, and that every house with Eisma (1979), no estimate is given in Table founded on 18 piles. This is less than the percentages ofall new dwellings in 1987 (9%), 1990 (7%), and 1995 (8%) 4.5(see Boonekamp 1994; de Graaf 1988; de Graaf 1996). Wall Wooden load carrying inner cavity walls seem to be quite4.2 popular in new residential buildings. Their market shareFloor was estimated at 20% of all dwellings built by housingWooden ground ¯oors have completely disappeared from corporations in 1995 (Beukema 1997). According to in-the OFD market (Eisma 1979e) and wooden ®rst ¯oors are formation of Buildsight however, the market sharerare in newly built houses. Excluding timber frame amounts to only 5% of the total area load-bearing innerbuildings, the market share of wooden ®rst ¯oors in 1990 walls in all new OFDs; this equals 57,000 m2 in 1996is estimated at 1 to 2% (Boonekamp 1994). This is in ac- (Buildsight 1997).cordance with the share of 1% which can be derived from It is unknown, how much wood is used for inner non-(Beukema 1997). In 1996, there was a total surface of bearing walls. A relatively small amount of timber, mostly329,000 m2 of wooden ¯oors in all new OFDs (3% of the spruce, is used in combination with gypsumboardstotal ¯oorarca in OFDs). The amount of beams necessary (Boonekamp 1994). For 1996 there are no data on woodis calculated from the ratio ¯oorarea ¯oorbeams in 1982. use in inner walls. In line with Eisma (1979) andFar out most popular for ¯ooring is sheet material like Boonekamp (1994) this wood use is neglected.oriented strand board, underlayment and plywood. It isassumed that the average thickness of the ¯ooring material 4.6is 15 mm and that the area of wooden (spruce) ¯ooring is Roofnil (see Table 2). From Buildsight (1997), it can be derived that the total surface of sloping roofs of OFDs in 1996 was 5,882,000 m2.4.3 With the ratio of wooden beams to roof area, the totalFacade amount of beams can be calculated. The 1996 market shareBuildsight lists 140,000 m2 of wooden facades, corre- of beams in sloping roofs is estimated at 90%.sponding to a market share for OFDs of 1.5%. Pre-fabri- For boarding of roofs, it is assumed that 75% of the totalcated facades often have wooden parapets. Buildsight gives sloping roof area of OFDs is boarded with plywood andno information on parapets; no estimate is given in chipboard, with a thickness of 15 mm. The wood use inTable 2, as the total surface is not known. In the period ¯at roofs in OFDs (504,000 m2 in 1996) is neglected.1980±1982 about 3,000 m3 of wood were used for parapets In 1996, 32% of all OFDs had a gutter boarded withrelated to window frames. In line with the data for 1987 wood products (Buildsight 1997), most of it plywood (deand 1990, indicating a market share of 50% for wooden Graaf 1988). Detached houses had a facade of 9.82 inparapets related to window frames in facades for all width, while an OFD in a row had a facade of 5.43 m indwellings (de Graaf 1988; Boonekamp 1995), the market width (Buildsight 1997). If the assumption is made that theshare of wooden parapets for 1996 is estimated at 50%. length of gutters is twice the width of the facade, an esti- Wood is market leader in window frames for new mate can be derived of the wood use for gutters in 1996.OFDs. According to (Buildsight 1997), the total window In 1996, 20.5% of all new OFDs had a dormer. Theframe surface in facades of OFDs built in 1996 was market share of wood is put at 50% (see Table 2). This1,246,000 m2, 92% of which was wood. The total market means an increase compared with the estimated 35%shares of wood for window frames in all dwellings in 1982, market share for 1990, in line with expert opinion1987, 1990, and 1995 were estimated at 95, 91, 85, and 90%, (Boonekamp 1994).respectively (de Graaf 1988; Boonekamp 1994; Boonekamp1995). Of the wooden frames applied in OFDs in 1996, 4.713% is coniferous and 87% hardwood according to DoorsBuildsight (see Table 2). This ratio is roughly in line with In 1996, 232,000 outer doors were used for all new OFDsestimates of Boonekamp (1995) who states that the ratio of (Buildsight 1997). It is estimated that of this total number
  6. 6. there were 25,000 doors for sheds and 10,000 doors to wood is put at 30:70 and for 1981 and 1982 70:30 and for garages. Furthermore it is assumed that 90% of all outer 1996 at 75:25. The above mentioned estimates are in line doors of OFDs are made of wood and that the ratio with the data reported by van der Werff (1984b) and es- hardwood to coniferous wood is 85:15. In 1987, of wooden timates by de Graaf (1988); Boonekamp (1994) and outer doors in all dwellings, hardwood had a share of 81% Boonekamp (1995). and coniferous wood of 9%. Merbau was by far the most Table 3 summarizes the total amount of wood products popular wood used for hardwood outer doors, followed by applied in OFDs built in the period 1969±1982 and in meranti (de Graaf 1988). 1996, as well as the calculated amount per OFD for these Most inner doors are made of spruce in combination years. For a good interpretation of the data derived from with plywood or chipboard. In 1996, the total amount of the QMD, it is important to realise that they are an average inner doors was 610,000 (Buildsight 1996). Using a con- from three categories of one-family dwellings, namely412 version factor, the total amount of wood used for inner Housing Act (HA) houses, Premium houses (P) and non- doors can be estimated. The total area of wooden inner subsidized houses. The ®rst two categories are more (HA) door frames in 1996 was 1,541,000 m2; this equals a market or less (P) subsidized by the government. It should be share of wood of 13% (Buildsight 1997). This percentage is noted that in the non-subsidized category, twice or even lower than the market share for wood of 20% of all thrice as much timber is applied as in Housing Act houses dwellings built in 1995 by housing corporations (Beukema (Eisma 1979) (NEI 1983). For this reason, the share of the 1997) but higher than the estimates for 1987 (de Graaf non-subsidized category within the OFD sector is also 1988) and 1990 (Boonekamp 1994): 10% and 5±10%, re- given in Table 3. spectively. Of the wooden inner door frames used in OFDs It should also be noted that for the period of 1969±1982, in 1996, 86% were made from hardwood, 14% of conifer- the wood use refers to OFDs built in 1970±1983. The ous wood (Buildsight 1997). In 1982, still 29% of the values for 1996 are representative for the OFDs built in the wooden inner door frames in all dwellings were made of same year. coniferous wood and 71% of hardwood (van der Werff It can be learnt from Table 3 that from 1969 to 1982, the 1984b), so between 1982 and 1996 coniferous wood lost total amount of wood products used in all OFDs is almost market shares at the cost of (mostly tropical) hardwood. constantly declining, the years 1976 and 1977 being the exception to the rule. In this period, a relative great vari- 4.8 ation in roofs was a fashion among architects, which may Staircases partly explain the higher average (van der Werff 1980). About 115,000 staircases were built into all new OFDs in Furthermore, in 1976±1979 the share of unsubsidized 1996 (Buildsight 1997). It is assumed that they are all made houses was relatively high, leading to a higher volume of from wood. It can be derived from de Graaf (1988) that in wood used in OFDs. In 1969, over half a million m3 wood 1987, of wooden staircases in all dwellings, hardwood had products were used in OFDs, while in 1982 and 1996 only a market share of 72% and coniferous wood of 18%. 200,000 m3 wood products were applied. In 1972, the year In Table 2, the estimates of the wood use per building with the highest number of OFDs planned, the total wood element in 1996 in new OFDs are given. To determine the use was also the highest of the 69±82 period. The total use amount of m3 per application, use is made of conversion of products of coniferous wood (mainly spruce) declined factors in line with de Graaf (1996) and Oskam (1995). dramatically in the period 1969±1982. For 1996, the total use of coniferous wood is estimated less than in 1982. The 5 application of hardwood reached its peak in 1976 and 1977 Total wood use in new OFDs and maintained a yearly level of about 30,000 m3. As far as The data from Table 1 can be converted into m3 wood sheet material (®bre/chip boards, plywood) is concerned, products and accumulated to coniferous wood, hardwood it should be noted that, due to changes in the documen- and sheet material (chipboard, plywood, soft- and hard- tation, a strange jump occurs in the data around 1978. This board). For the determination of conversion factors, use is is related to a modi®ed calculation method of the boarding made of information in Oskam (1995); de Graaf (1996). of roofs, being the main outlet for sheet material. As to the kind of wood product, it should be noted that Coniferous wood was, in 1969, by far the main category, for kitchen/terrace/balcony doors and for staircases to the accounting for more than 92% of the total amount of ®rst ¯oor, the assumption is made that in the period be- wood, while in 1982 this share had declined to just over fore 1976 the ratio between hardwood and coniferous 50%. In 1996, coniferous wood makes up 48% of all wood wood was 20:80 and afterwards 80:20. For staircases to the products applied in OFDs. In 1969, solid tropical hard- ®rst ¯oor, the ratio between hardwood and coniferous wood had a share of only 3% of the total amount of wood wood is estimated at 20:80. For pivotal windows, the as- used in OFDs. In 1996, 14% of all wood products in OFDs sumption is made that until 1975 all of them were made were made from solid tropical hardwood. For sheet ma- from coniferous wood, after 1975, 10% is assumed to be terial (in 1969 mainly ®breboard, chipboard and plywood) made of hardwood. For wooden dormers, the assumption the share increased from 5% in 1969 to 38% in 1996 is made that until 1975 all of them were from coniferous (mainly chipboard, OSB and plywood), with a notably wood, after 1975, 80% is assumed to be made of hardwood. strong increase in chipboard during the seventies. For wooden inner door frames the assumption is made Per OFD, the average wood use dropped from 6.19 m3 that until 1975 they were all made of coniferous wood, in 1969 to 3.22 m3 in 1982 and 3.35 m3 in 1996. Excluding between 1976 and 1980 the ratio hardwood to coniferous wooden foundation piles from the analysis in 1969,