CONTENTS. Commentary on construction implications. Estimated Construction Costs for Varying Cavity Thicknesses. Rev C

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Sheena Gladys Stephens
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2 CONTENTS Section 1 Introduction Section 2 Commentary on construction implications Section 3 Estimated Construction Costs for Varying Cavity Thicknesses Section 4 Notes and Exclusions Appendix A House Type Drawing

3 SECTION 1 INTRODUCTION The purpose of this report is to assess the cost implications, in domestic construction, of incorporating increased cavity thicknesses in lieu of the conventional 100mm cavity construction. The thicknesses considered in this exercise are 175mm and 200mm. It should be noted that, for the purposes of this report, the costs of cavity insulation have been excluded. The use of Low conductivity ties has also been considered for each option as an alternative to alleviate thermal bridging problems with wall ties at wider cavities. The costs compiled in this report for each option are based on a typical semidetached house the layout of which was provided by the Client. The estimated costs for each option have been calculated and tabulated to express the costs as extra-over the corresponding costs for a conventional 100mm cavity construction. Costs have been based in price levels current in the Southern England

4 SECTION 2 COMMENTARY ON CONSTRUCTION IMPLICATIONS In the calculation of estimated costs for this report, traditional cavity construction has been assumed. Traditional 1 metre deep strip foundations in normal ground conditions have been assumed. External walls have been assumed as 100mm blockwork internal skin with 100mm facing brick skin. General The elements affected by the varying cavity thickness are listed below; Substructures - Increased volume of excavation and disposal from site; increased concrete cavity fill and increased threshold thickness. External walls increased area of external skin, cavity closing at tops, revised jamb closing detail, increased concrete sill depth; revised cavity wall tie specification (Note for purposes of constructional practicality the party wall cavity thickness and wall tie specification have been assumed the same as the main external cavity walls) Finishes - Increased plaster to reveals; increased paint to reveals Roof - Increased area of roof tiles, felt and battens; increased rafter/truss length and increased ceiling joist/truss length Structural In the assessment of the constructional implications associated with varying the cavity thickness we approached RPS Consulting structural engineers to obtain input on structural implications. After reviewing the specific house layout and the proposed cavity widths, RPS have confirmed that these would require no additional structural measures in the form of piers or wind-bracing etc. Note: Other layouts may be subject to structural implications.

5 3.03 ESTIMATED ADDITIONAL COST FOR 175MM IN LIEU OF 100MM CAVITY CONSTRUCTION FOR TYPICAL SEMI-DETACHED HOUSE TYPE (INCLUDING LOW CONDUCTIVITY TIES) Substructures DESCRIPTION Qty Unit Rate Total Excavate trenches not exceeding 2m deep 2.45 cu.m Disposal of excavated material off site 2.45 cu.m C20 in-situ concrete filling to cavities 1.84 cu.m Increased depth of precast concrete threshold; 265 x 140 in lieu of 240 x m External Walls 100mm thick facing brick external skin of cavity wall 5.41 sq.m Increased specification of cavity wall ties from ST1(225) to Teplo 2 (325) sq.m mm mineral fibre board closing cavities at tops of cavity walls; 325 wide in lieu of 300 wide m Purpose made steel lintels to suit wider cavity in lieu of standard steel lintels 9.90 m Proprietary cavity closers; at jambs; 275 wide in lieu of 200 wide blockwork m Increased depth of precast concrete sills 265 x 140 in lieu of 240 x m Increased cavity dpc width 2.12 sq.m Total carried forward 1,472.98

6 3.03 ESTIMATED ADDITIONAL COST FOR 175MM IN LIEU OF 100MM CAVITY CONSTRUCTION FOR TYPICAL SEMI-DETACHED HOUSE TYPE (INCLUDING LOW CONDUCTIVITY TIES) Finishes Total brought forward 1, Coat plaster to blockwork walls; increased 25mm width 3.00 sq.m undercoat; two coats emulsion paint to plaster walls 3.00 sq.m Roof Concrete roof tiles; untearable felt and 50 x 35 softwood treated battens 2.94 sq.m x 38 softwood treated rafters m x 38 softwood joists m x 19 redwood treated fascia 0.60 m x 12 Ext grade plywood soffit 0.60 m TOTAL 1,699.24

7 3.04 ESTIMATED ADDITIONAL COST FOR 200MM IN LIEU OF 100MM CAVITY CONSTRUCTION FOR TYPICAL SEMI-DETACHED HOUSE TYPE (INCLUDING LOW CONDUCTIVITY TIES) Substructures DESCRIPTION Qty Unit Rate Total Excavate trenches not exceeding 2m deep 3.36 cu.m Disposal of excavated material off site 3.36 cu.m C20 in-situ concrete filling to cavities 2.21 cu.m Increased depth of precast concrete threshold; 265 x 140 in lieu of 240 x m External Walls 100mm thick facing brick external skin of cavity wall 6.76 sq.m Increased specification of cavity wall ties from ST1 (225) to Teplo 2 (350) sq.m mm mineral fibre board closing cavities at tops of cavity walls; 325 wide in lieu of 300 wide m Purpose made steel lintels to suit wider cavity in lieu of standard steel lintels 9.90 m Proprietary cavity closers; at jambs; 275 wide in lieu of 200 wide blockwork m Increased depth of precast concrete sills 265 x 140 in lieu of 240 x m Increased cavity dpc width 2.80 sq.m

8 3.04 ESTIMATED ADDITIONAL COST FOR 200MM IN LIEU OF 100MM CAVITY CONSTRUCTION FOR TYPICAL SEMI-DETACHED HOUSE TYPE (INCLUDING LOW CONDUCTIVITY TIES) Total carried forward 1, Finishes Total brought forward 1, Coat plaster to blockwork walls; increased 25mm width 3.75 sq.m undercoat; two coats emulsion paint to plaster walls 3.75 sq.m Roof Concrete roof tiles; untearable felt and 50 x 35 softwood treated battens 3.50 sq.m x 38 softwood treated rafters m x 38 softwood joists m x 19 redwood treated fascia 0.80 m x 12 Ext grade plywood soffit 0.80 m TOTAL 2,070.95

9 SECTION 4 NOTES AND EXCLUSIONS Notes 1 Costs have been based on pricing levels current in Southern England 2 No allowance has been made for abnormal ground conditions 3 Only elements directly affected by the variation in cavity width have been included in the costs comparison tables 4 For the purposes of this report, no consideration has been taken of any implications to the mechanical and electrical installations due to differing u-values etc resulting from the varying cavity and insulation thicknesses in each option. Exclusions The following are specifically excluded 1 Professional fees 2 VAT (Normally zero rated for new-build domestic construction) 3 Planning and Building Control fees 4 Statutory fees and charges 5 Legal fees 6 Finance costs

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