ARC401 report

ARC401 REPORT
Principles of Construction Technology
Student No. Q12248606
Abstract
On another part of the site the developer intends to build 3 storey flats
instead of individual houses, with one flat at ground floor level and a
second flat incorporating a room in the roof above:

ARC401 - PRINCIPLES OF CONSTRUCTION TECHNOLOGY
Contents:
1.0 - Introduction
2.0 - Assessment Question 1 Page 1
Appendix Page 19
References Page 20
Bibliography Page 21

1
Introduction:
This report has been prepared on behalf of the ‘Local Developer’. Its purpose is to provide a
suitable foundation type and floor construction for a new 3 storey building that is to provide 2
flats with the ground floor compromising one dwelling and the first floor to provide the
second dwelling, incorporating a room in the roof above. Details of the construction will be
provided within the report and these are produced using Archicad and drawn by the author
of this Document.
Assessment Question 1:
2.0 Ground Investigations on site have identified the soil type to a firm clay soil. This will
therefore be taken into account when specifying the floor construction. Due to the nature of
clay based soils, heave is a possibility and a suitable floor construction needs is required to
deal with this. The BRE Digest part 241, gives a brief explanation of the process, causes
and problems of heave: ‘Volume changes in clay soils brought about by seasonal changes in
soil moisture content and by the removal of soil moisture by deeply rooted vegetation have
caused widespread damage to low-rise buildings, especially following periods of low rainfall.’
(BRE Digest 241, 1990).
2.1 A ground bearing slab would be inappropriate for this development because heave
will force the slab to bend up through expansion or subside downwards due to shrinkage.
This can result in the floors integrity being damaged and also can result in horizontal forces
against the lower sections of wall and upper portion of the foundations.
2.2 The NHBC states that shrinkable soil, expansive materials or other unstable soils will
require the use of a suspended floor construction. It also goes on to say where the soil type
consists of more than 35% fine particles and has a plasticity of 10%, the soil can be classed
as a shrinkable soil. A soil-testing laboratory is required to confirm this value. (NHBC Part
5.1, Substructure and Ground bearing floors).
2.3 A suspended floor will be used in the form of a precast beam and block floor make-
up as this removes the reliance of the floor construction bearing on the ground and focuses
its loads onto the loadbearing walls. A ventilated void must be provided below the beam and
block floor with a clear depth of at least 150mm. The beam and block floor is to be coated
with a slurry mix to receive a 1200 gauge damp proof membrane as noted in A. D. Part 4.19.
The floor will be insulated using 60mm Kingspan Kooltherm K3 Floorboard. A separation

2
layer (polythene sheet not less than 500 gauge) is to be laid on top of the insulation with a
65mm glass fibre reinforced screed. (www.Kingspaninsulation.co.uk, 2016) Refer to Figure
1 for Floor Build-up.
2.4 For the foundations, the BRE states that the accepted recommendation of a 0.9m
deep trench is enough to eliminate significant seasonal ground movement. This is only
applicable for ‘open’ ground sites where no trees, bushes or hedges are located within close
proximity of the building. The site in question has no existing major vegetation so can be
classed as Open Ground allowing this method to be adopted but give added tolerance the
use of a 1m deep foundation is to be used. This can be referenced back to Approved
Document A section ‘2E4’.
2.5 With the depth now calculated, using GBG 39, part 2 which refers back to Part A of
the Building Regulations, the other foundation requirements and sizes can be calculated
whilst also taking the BRE Digest 241 into account. Between foundation types we had the
ability to use strip, trench-fill or piles to achieve the loading required.
2.6 The BRE Digest 241 has a costing comparison table that compares all three of these
foundation types at a depth of 1m. Narrow strip (trench fill) and Bored pile and beam come
out at a similar price with Deep traditional strip being roughly 25% more expensive. This is
due to the increase of skilled labour required by traditional strip foundations as the brickwork
is built up out of the trench from the top of the foundation requiring several courses of
brickwork to be built. Also for safety reasons, this is also unsuitable to use. Although bored
pile and beam is cheaper, in this circumstance, the GBG has been recommended as our
basic resource and does not cover this type of foundation. Therefore the use of trench fill is
the most appropriate.
2.7 By using GBG 39, see Appendix A, it can be assumed that using floor constructions
of a beam and block ground floor construction and a precast concrete 1st
floor (due to
dwelling separation and party floor requirements) table 1a applies as in Appendix A. From
this the foundation type can be determined as E. This is taken through to table 4 which then
allows the use of this letter with the type of soil conditions which are firm clay giving a
foundation width of 750mm. The GBG breaks up Table 10 from Approved Document A into
a more approachable format allowing the creation of a rough loading using floor types and
floor sizes.
2.8 In conclusion, it is summarised that the floor type should be a suspended beam and
block construction with the foundation for the rear wall being 1000mm deep, as discussed in

3
2.4, 750mm wide as discussed in 2.7 and the concrete fill coming up 375mm below finished
ground level resulting in 625mm deep concrete foundation.
Figure 1-Foundation and floor construction of the rear wall of the dwelling.
3.0 A cold roof by definition is a roof where the insulation is either attached directly to the
bottom of the roof joists or located in the ceiling joist level (www.Kingspaninsulation.co.uk,
2016). They require cross ventilation above the insulation to allow the roof to breath as set
out by Approved Document C. The insulation shown in the provided detail shows the
insulation between and above the ceiling joists. This means that the space above, inside the
roof space, will be cold as the insulation will prevent the majority of the warmth rising through
the building. This creates a point where interstitial condensation can occur if the roof is not
adequately ventilated or an adequate vapour permeable underlay is not present. The use of

4
a vapour control layer below the insulation, on the warm side of the roof, can also be used to
prevent the passsage of moisture through the insulation.
3.1 Interstitial condensation occurs within the building’s fabric, for example the insulation,
and is where warm moist air meets cold dry air and condenses into water droplets as the
moisture cools. This can occur within, or on top, of the insulation if appropriate measures
are not undertaken, for example adequate ventilation to the space above the insulation.
3.2 If ventilation is not provided to the neccessary specification, as set out in Part C of
the Approved Documents, then this can result in the build up of condensation within the
insulation. This can also penetrate the ceiling and cause damp issues, as well as causing
the insulating properties of the insualtion to fail resulting in a cold bridge allowing
condensation to build up on the underside of the ceiling.
3.3 Warm Roofs don’t have the same ventilation requirements that cold roofs have to
meet in order to avoid condensation. The insulation is located between, or between and
above the rafters with ventilation provided by counter-battens fixed to the rafters through the
insulation. This provides the necessary ventilation without having to take steps to ventilate
at the eaves below the sarking membrane. The wall can be closed with a cavity closer and
compacted loose fill insulation can be used to fill the gap between the closer and the
insulation in the rafters. Cold roofs on thee other hand require a 50mm air gap which is
often missed by the site team and stops the cross-flow of air allowing the air to become stale
and increase the chances of the roofs insulation failing as the moisture build up is not being
removed.
3.4 Figure 2 shows an alternative detail to the one provided, having been changed to
accommodate a room in the roof. The insulation is no longer located in the ceiling joist
beneath the room-in-the-roof because the warm air can now be allowed to enter the loft
space to help warm the room-in-the-roof. The use of dwarf walls help create a usable space
within the loft by reducing the size of the roof void whilst removing the lower edges/corners
of the room that would be impossible to use or maintain otherwise.
3.5 The insulation is now run in the dwarf wall and within the rafters above the usable
space. Heat can still escape from around the outsides of the dwarf wall so this section of
ceiling joist is insulated as normal with a layer of insulation between and above the joists to
the relevant size as stated by Kingspan to achieve the U-value of 0.20 as required by the
Approved Document C, 2.35:Table 2.

5
3.6 The construction of the floor for the room in the roof uses two steels running
perpendicular to the gable walls to provide the support required as the loading of habitable
rooms are different to that of a loft space. These steels support the dwarf walls which in turn
provide to support the roof. The timber floor joists are notched into the steels allowing the
use of a lower grade and smaller sized timber joists from the steels to the eaves/wall plates.
3.6 Roof constructions for new builds require a U-value of 0.20 W/(m2
K) as stated in
Approved Document C, 2.35:Table 2. This can be achieved using Kingspan as the
insulation provider. Using their Kooltherm K7 Pitched Roof Board, at 50mm depth in
conjunction with their 62.5mm Kooltherm Insulated Plasterboard with integral vapour control
layer, this achieves a U-Value of 0.19 with Stud centres of 600mm.
(Kingspaninsulation.co.uk, 2016)
3.7 The use of a proprietary eaves ventilator ensures that there is the minimum 50mm air
gap between the insulation and the roof finish/sarking membrane as required by the Building
Regulations Part C. The minimum air gap allowed between rafters is 25mm clear where the
sarking membrane may have draped as required in BS 5250: H.3.2.
3.8 Due to the roof pitch being more than 35o,
ridge ventilation must also be provided as
stated by Approved Document C. In this case as shown in figure 3, the use of propriatory
ridge vents built into the dry-fix ridge detail provides the necessary ventilation to comply with
Approved Document C.
3.9 In conclusion, the construction details shown in figures 2 and 3 will provide not only
adequate insulation as required by part L of the Approved Documents and discussed in 3.5-
3.6, but also the necessary ventilation as required by Part C of the Approved Documents, as
discussed in 3.7-3.8.

6
Figure 2-Eaves and Dwarf Wall Detail for Room-in-Roof
Figure 3-Ridge Detail for Room-in-Roof

7
4.0 The raking abutment at the rear of the building allows the potential for water ingress
to occur. The raking abutment in question is displayed in figure 4. This is where moisture is
allowed to get into the building where the roof abuts the wall. It can lead to issues involving
damp which can damage internal finishes and even impair the structural stability of a
building if not avoided.
4.1 The solution to avoid water ingress is to use a lead flashing to code 4 to BS 5534:
Table 5, p22, in conjunction with lead soakers at code 3. This prevents water ingress by
creating a protective barrier at the abutment. The use of double-lap tiles makes the use of
soakers and a flashing the appropriate means to protect against the water ingress.
4.2 Flashing sheets can not be cut below the water line which runs parallel to the roof
slope at 65mm away from top of the tiles. A further 85mm line provides position where the
lead is to be turned into the relevant bedjoint. The lead has to be folded into the joint 25mm
and return on itself to prevent water tracking along the lead into the cavity. Lead flashing
sheets can be a maximum of 1.5m in length. With 100mm lap between sheets. As shown in
figure 12.
4.3 The soakers are an L shaped piece of lead with length = lap+gauge+25mm so are
dependant on the type of tile used and are generally 100mm wide with the height being the
tile height in construction + 65mm. as shown in figures 6, 10 and 11.
4.4 The Soakers are installed first during the tiling process starting at the eaves. The
lead flashing then overlaps this and is then turned into the bedjoint as shown in figure 7, 8, 9,
12 and 13. NOTE: The figures are in order of construction/assembly. This provides the
required protection against water ingress as required BS: 5534.
4.5 The cavity within the wall also needs protecting due to the opening below the roof.
Where the lintel is installed, any water that enters the cavity would run off of the lintel, or
through in some cases, and enter the habitable space of the building. The lintel used is
depicted in figure 14 and 15. To avoid this, a series of stepped cavity trays that can be
proprietary plastic with 3 different piece types making up the run. An open ended tray is
used above the ridge with the next step down having a closed end on the edge closest to the
roof as shown below in figure 5 and figure 8. Figure 8 shows a 3D construction using this
system. The trays overlap by ~100mm so that any water dripping off the tray hits the one
below and is taken away from the structural opening. (Cavitytrays.co.uk, 2016)

8
4.6 The last end tray is closed at both ends and funnels the water out of the cavity
through a series of weep holes (not shown), onto the abutting roof.
4.7 In conclusion the lead soaker and flashing will provide the protection that is required
by the Building Regulations as addressed in 4.0-4.4. The cavity closers will in the given
configuration as addressed in 4.5 and 4.6
Figure 4 – Drawn in Archicad 19 – the raking abutment

9
Figure 5 - Cavity Tray Arrangement
Figure 6 - Lead Soakers installed

10
Figure 7 – Lead Flashing installed over soaker and folded into bed joint below DPC
Figure 8 – Depiction of finished flashing detail with installed cavity trays/DPC’s

11
Figure 9 – Final finished roof with DPC, lead flashing and soakers installed
Figure 10 – Cross section of soaker and flashing joint between tile and brickwork.

12
Figure 11 – Lead soaker sizing and installation detail
Figure 12 – Lead Flashing sizing and installation Detail

13
Figure 13 – Lead Flashings installed over soakers

14
Figure 14 – Cavity tray within wall.
Figure 15 – Cross-section of lintel within wall construction.

15
5.0 The area behind the house is to be used by the local car mechanics firm to construct
a new garage to expand into. This requires a portal frame structure of around 6m high and a
clear span of around 15m. The sizing and loading of the portal frame is to be carried out by
the appointed engineer’s, with the provided details and construction subject to their steel
specification.
5.1 The sizing of the concrete pad foundation can be achieved by following BS
8004:2015. This can produce the required dimensions but this cannot be achieved without
the engineer’s calculations on steel sizing and loading of the structure. For illustrative
purposes a foundation depth of 1000mm and a width of 1000mm has been used.
5.2 With the use of the building being a car mechanics, the insulation is placed below the
slab as a traditional screed would not offer enough strength and would be susceptible to
impact damage. The concrete slab is cast on top of a DPM, on a sand blinding, on a
compacted hardcore sub-base.
5.3 The slab insulation is brought up to meet the insulation within the cladding eliminating
any cold bridge potential. The steel stanchion is bolted into the concrete pad with an anchor
plate cast in the pad. The steel is raised off of the pad by ~50mm using packers to allow for
differences in the heights of the foundations in relation to the structural frame. The voids
below the stanchion baseplate is to be fully grouted. See figure 16.
5.4 The cladding used has integral insulation to improve build efficiency and this is to
Kingspan’s specification supported on steel girts at suitable centres. A 1000mm high
reinforced concrete stall riser panel is to be tied to the steel with the panel starting at
foundation level. The concrete stall-riser panel will be cast in-situ using formwork and
reinforced with steel rebar. Insulation is to be placed between the steel stanchion and the
stall-riser.
5.5 The insulation is returned across the top of the panel to eliminate any cold bridges
and joins up with the Kingspan cladding panel. At the eaves, the same cladding has been
used on the roof for consistency and is suspended off of the rafters using ‘C’ section purlins
bolted to the cleats. The external wall cladding has been brought up to the same level as
the roof finish to allow for the 150mm deep box gutter laid to falls. See figure 17. The roof
slope is 6o
which is typical for portal frames. (Steelconstruction.info, 2016)

16
5.6 The ridge has a simple ridge cover mechanically fixed to the purlins to keep it
secured in place. This provides the overlap required to stop water getting through the
connection between the roof finishes on either side. As shown in Figure 18.

17
Figure 16 – The foundation and cladding of the industrial building

18
Figure 17 – The portal frame at eaves level.
Figure 18 – The portal frame at ridge level.

19
Appendix A:
British Research Establishment, 2001, Simple foundations for low-rise housing part 2,
in: Anon, The Good Building Guide, London, CRC Ltd.

20
References:
• Construction Research Communications Ltd, 1997, Low-rise buildings on Shrinkable
clay soils: Part 1. In: Anon, BRE Digest 240, ed. 2, London, Construction Research
Communications Ltd, 1-4

21
• Construction Research Communications Ltd, 1997, Low-rise buildings on Shrinkable
clay soils: Part 2. In: Anon, BRE Digest 241, ed. 2, London, Construction Research
Communications Ltd, 1-4
• BRE, 2006. BR 443 Conventions for U-value Calculations. [online] Available at:
https://www.bre.co.uk/filelibrary/pdf/rpts/BR_443_(2006_Edition).pdf [Accessed 5
Jan. 2016].
• Kingspaninsulation.co.uk, (2016). Kingspan Insulation - Roof, wall, floor, and HVAC
ductwork insulation. [online] Available at: http://www.Kingspaninsulation.co.uk/
[Accessed 5 Jan. 2016].
• BSI Standards Institute, 2015. BS 5534: Slating and tiling for pitched roofs and
vertical cladding – Code of practice, , 8th ed. London: BSI Standards Institute
• Steelconstruction.info, (2016). The Steel Construction Information System. [online]
Available at: http://www.steelconstruction.info/ [Accessed 7 Jan. 2016].
• Kingspanpanels.co.uk, (2016). Kingspan Insulated Panels UK & Ire. [online]
Available at: http://www.Kingspanpanels.co.uk/ [Accessed 7 Jan. 2016].
• The Building Regulations, 2013, Approved Document A – Structure, ed. 2013,
London, HM Government.
• The Building Regulations, 2013, Approved Document C – Site preparation and
resistance to contaminants and moisture, ed. 2013, London, HM Government.
• The Building Regulations, 2013, Approved Document F– Ventilation, ed. 2013,
London, HM Government.
• The Building Regulations, 2013, Approved Document L1A – Conservation of fuel and
power, ed. 2013, London, HM Government.
Bibliography:
• The Art of Construction, Building on Clay, 1976, Construction Detailing.
• Glidevale.com, (2016). Glidevale. [online] Available at: http://www.glidevale.com/
• Cavitytrays.co.uk, (2016). Type X Cavitray - Cavity Trays Limited. [online] Available
at: http://www.cavitytrays.co.uk/damp-proofing/view/1/163/7/type-x-cavitray

22
• Calderlead.co.uk, (2016). Lead Products | Lead Engineering | Calderlead. [online]
Available at: http://www.calderlead.co.uk [Accessed 6 Jan. 2016].
• Britishlead.co.uk, (2016). British Lead – Basic fitting details. [online] Available at:
http://www.britishlead.co.uk/downloads/basic-fitting-details-no8.pdf [Accessed 6 Jan.
2016].
• Glidevale.com, (2016). Glidevale. [online] Available at: http://www.glidevale.com/
• Steelroofsheets.co.uk, (2016). Industrial Roofing and Cladding | Accord Steel
Cladding. [online] Available at: http://www.steelroofsheets.co.uk/categories/industrial-
cladding/ [Accessed 7 Jan. 2016].
• Leadsheet.co.uk, (2016). The Lead Sheet Association - Technical Advice & Skills
Training on Rolled Lead Sheet, Lead Sheet Manufacturers and lead sheet
characteristics. [online] Available at: http://leadsheet.co.uk/ [Accessed 7 Jan. 2016].

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