INSULATION FOR WARM ROOFS

Insulation ~

Roofs absorb or reflect heat according to the position of their colour in the spectrum. Black absorbs the most heat, then dark green, blue and violet whereas red, orange, yellow and ultimately white reflect heat. However in practical terms in UK, while fresh silver paint may assist in reflecting some heat the dominant maintenance free way to maintain a more constant temperature is with insulation]. To prevent heat loss (and gain in summer) insulation should be installed in new or upgraded roofs per the relevant Building Regulations. Particular cognisance needs to be given to the 2002 edition of the Approved Document L: (L1 Conservation of fuel and power in dwellings and L2 Conservation of fuel and power in buildings other than dwellings) for England and Wales which came into effect on 1/4/02. New buildings should comply with British Standards, typically insulation or “U-Values” of 0.25 W/m2K. This can be met with thicknesses of 90 to 96 mm of foamed insulation such as Kingspan when fitted in accordance with the relevant Warm Roof specifications below.

Warm Roofs / Cold Roofs / Inverted Roofs ~

In a cold roof construction the insulation is laid immediately above the ceiling. The roof deck and the void between the joists are at or close to the outside temperature. It is likely therefore warm humid air coming from inside the building will condense within the cold roof space. To prevent this a vapour barrier (polythene or aluminium foil) needs to be laid on the underside of the insulation to stop the water vapour penetrating into the roof void. Care must be taken not to breach this barrier with service pipes and cables. Also as some air leakage is likely, Building Regulations require that cross-ventilation is created. This needs to be achieved by creating a space between the insulation and the deck of 50mm and providing cross ventilation on two opposite sides of the roof by permanent vents of an area equal to that of a continuous gap of 25mm wide along the full length of those sides. (For full details consultation with Building Control is suggested). Cold Roof construction has largely been superseded by Warm Roof Construction.

In the warm roof construction a vapour barrier is laid immediately over the roof deck, followed by the insulation material and waterproofing membrane. The insulation must withstand the roof loads and proprietary roof insulations meet this requirement and the newly introduced U-Value. The thickness needs to be such that all materials below are sufficiently warm to stop condensation. The decking and insulation must be sufficiently well fixed to prevent movement which could damage the waterproof membrane. The specification and notes given below meets these requirements.

In an inverted roof construction, a special type of insulation is laid on top of the waterproofing membrane which itself is laid on top of the roof deck. The whole roof is hence not only insulated but protected from the elements, sun and mechanical damage caused by pedestrian traffic. The insulation itself needs to be weatherproof and non-absorbent and is covered with a filter sheet to prevent the ingress of excessive organic material (and is usually covered by shore or river washed pebbles or pavers suitably mechanically isolated  to prevent scuffing, wind or similar damage to the surface. Treated wooden decking may not give UV protection to the insulation or ballast sufficiently. Also they should only be used after isolating over membranes which have been fully boned or mechanically fixed. Consideration needs to be given to possible leak detection and dead weight loads on the roof structure.

It can be concluded from the above that:

WARM ROOFS CONSTRUCTED TO THE SPECIFICATION BELOW ARE A SIMPLE RELIABLE SOLUTION TO PRACTICAL PROMLEMS POSED WHICH MEET BUILDING REGS

Benefits

TYPICAL WARM ROOF DETAIL

The figure shows a typical warm roof construction for flat roofs (10o slope or less) consisting of:-

1)   12 mm of skimmed plasterboard secured with galvanised clout nails to the underside of 150mm deep sawn timber floor joists spanned at 400 mm centres with restraining herring bone strutting. The top of the joists unless generating an incline themselves will need to be capped with firring (or furring) pieces (usually long tapered pieces of timber [tapering to 12 mm minimum thickness]) to give a “fall” on the roof for drainage of 1 in 60 minimum. 
Note ~ If plasterboard is not fitted, then the Kingspan TR27 thickness needs to be 95 mm.

2)Joists overlaid with 18 mm roofing quality plywood conforming to BS 5268 (structural use) or Oriented Strand Board (OSB) grade 3 or 4 (structural grade) to form the deck well fastened to the joists. Timber cross noggings should be used to ensure that no edges of the deck are unsupported.

3)  Deck coated with Primer and when dry overlaid with 1 mm thick Self-Adhesive Foil Vapour Barrier (with release film removed) placed on the warm side so as to exclude any water vapour passing through the inner lining from the inside of the building which might condense causing wet rot and reduction in insulation efficiency etc.
Note ~ If Kingspan TR31 is used (which requires mechanical fixing) then no separate vapour barrier is needed as this product contains its own vapour barrier.

  4)   Vapour Barrier overlaid with Kingspan giving ‘U’ value of 0.25W/m2K per BS EN ISO 6946)    There are 3 panels per pack, each panel is 1200 x 600 x 90/96mm (0.72 sqm / panel). Either of the following systems can be used:-
        90 mm of Kingspan TR27 ~ Each side is “tissue” covered and the panel being symmetrical can be laid either way up. and they can be bonded with PU Adhesive (water foaming) spread over the surface with insulation panels lightly butted together and staggered in one direction. PU adhesive can be applied to the foil vapour barrier surface only (not the insulation board as well) from a 1.0 litre (1.3 kgs) container by cutting its nozzle to give a 12 mm bead which should be applied @ nominal 200 mm centres giving a distribution of 200 gms / sqm working within 5 to 35oC. So a practical typical pitch of the beads across a 600 mm panel would therefore be in mm approximately:-
Edge : 50 : 165 : 165 : 165 : 50 : Edge. = 80 gms / panel : 1 litre covers 16 panels.
Once applied beads should be over-misted if necessary with 5% water (based on adhesive weight). The panel is applied as soon as possible and within 1 hour maximum.
Mechanical Fixing ~ Instead of bonding, TR27 panels can be mechanically fixed incorporating a washer plate 75mm diameter or 70 x 70 if square ~ the minimum number of fixings for each board is 4 placed >50mm and <150 from edges and corners (ie 5.55 fixings/sq m on 1200 x 600 boards. However the exact number of fixings will vary with the location, size and other factors. 



96 mm of Kingspan TR31 ~ No 18 mm timber decking board or separate vapour barrier is needed as this product contains a vapour barrier and has a plywood surface. Boards should be laid along the joists and board joins staggered and butted with c2 mm gap with bearing surfaces of 20 mm min. Noggings should be fitted as necessary to ensure all board edges are supported.
Vapour proof non-setting gungrade mastic sealant must be applied continuously to the upper surface of all joists / noggings corresponding with insulation board edges to provide continuity of foil vapour control layer. A bead wide enough to accommodate two board edges butted side by side should be applied to the upper surface of all supporting joists and noggins. 
The board is mechanically retained with 140 mm x 4.8 mm dia purpose designed posidrive fasteners driven through the plywood ensuring heads are flush with the plywood surface. Screws should be driven in at 200 mm centres around the board edges and at 300 mm centres along any intermediate supporting timbers. Fixings should be staggered and not less than 10mm from board edges and not less than 50 mm from board corners and should penetrate timbers by 35 mm minimum and not overscrewed and be flush with the plywood surface. Screws must be staggered where two boards share a joist
 
5)   Insulation covered with either of the following EPDM systems:-                       
    SELF-ADHESIVE SYSTEM ~ Apply Primer and after allowing to dry, apply 2.5mm thick Self-Adhesive EPDM and seal all edges with a hot air gun.
    ONE PIECE SYSTEM ~ Apply water based Decking Adhesive to insulation with roller, roll rubber onto adhesive and firm into place with roller / soft broom etc.

Notes ~ For full instructions see DIY EPDM Rubber Roofing Guide & Kingspan data sheets for TR27 & TR31
      ~ Mechanical fixings are not recommended for balconies ~ use bonded Kingspan TR27.
  .   ~ If plasterboard is not fitted precautions must be taken to ensure protruding fastener points are not a hazard
       ~ If other insulation boards are used they must have a timber or other compatible surface.
       ~ All roof elements need protection against ingress of moisture during construction. 
       ~ If ballast is used instead of adhesives for either of the above systems then a 50 mm minimum deep layer of 16 to 32 mm diameter of river or shore washed pebbles or equivalent weight paving stones (“pavers”) should be used. Any pavers or garden decking should be isolated from the surface of the rubber to prevent potential chaffing damage. Garden Decking should only be used where the membrane and insulation (if used) are fully boned or mechanically fixed - not loose laid.
      ~ Any adhesives need also to be isolated from the rubber membrane surface to prevent possible degradation of the surface.
      ~ EPDM paints should be used if over-painting for cosmetic purposes is required (available in silver grey and stone grey paint colours).
 

MATERIALS SCHEDULE

TR27 Insulation ~ Available in packs of 3 panels each panel is 1200 mm x 600mm x 90 mm
      @ £12.50 / sq m each pack of 3 panels is 2.16 sq m = £27.00 / pack
Minimum sale 2 packs, sold in complete packs only.
Transport costs per pack of 3 panels £15.84 + VAT (11.3 kgs / pack of 3)
If over 5 packs then £78.00 for whole delivery of insulation within 100 miles of                
Hereford, elsewhere please ask. (16 packs = c34.56 sq m = 1 pallet load).
 
PU Adhesive ~    Cost is £0.50 / 600 x 1200 mm panel = 0.72 sq m (80 gms of adhesive/panel).                         Minimum purchase covers 14 panels @ £7.00 / 1.1 litre pot
Mechanical Fixings ~ 140 long x 4.8 diameter Posidrive coated self-drilling screws ~ £20.00/100
       ~ 70 x 70 mm steel insulation retaining/load-spreading plates ~ £ 7.71/100
Self-Adhesive Foil Vapour Barrier ~ £6.63 / sqm (30m / roll x 1m = £198.90 / roll
Vapour Proof Non-Setting Gungrade Mastic Sealant ~ £4.85 / 380 ml cartridge.
Corner Cloaks ~ Internal and external corner pieces for EPDM Membrane £4.40 each
Primer ~ For EPDM Membrane, Vapour Barrier or Cloaks £5.70 / 0.5 kg tin, larger sizes available
Impact Adhesive ~ For Corner Cloaks £9.56 / 1 kg tin
Thinners ~ For cleaning Corner Cloaks £8.20 / 1 kg tin

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