Cold roof insulation with rigid PUR foam (by IsoSpray)

Last Updated on: 15th November 2020, 10:06 pm

UK rigid foam insulation specialist IsoSpray roofing and insulation contractors use polyurethane spray foam for insulating cold roofs. After the system is installed a warm roof will have been created that helps prevent condensation. The spray foam also has the benefit that it will bond all slates and tiles on a pitched roof where nail fatigue is causing slippage. The rigid high density foam will bond all slates and tiles and prevent any future movement and slippage. The result is a stable roof and an efficient rigid roof insulation system that will conserve energy.

How long does it take for polyurethane spray foam to dry / cure?

The rigid polyurethane foam is typically sprayed applied by heavy duty industrial compressors at 125 and at a pressure of 600 psi. This ensures both excellent adhesion and effective coverage in all nooks and crannies. The polyurethane spray foam cures within a short time and is hard within an hour. The spray foam is typically applied at a nominal depth of 40 mm. 25 mm is usually the minimum depth and this would provide a good anti- condensation coating by creating a warm roof.

Higher depths can be applied to increase the level of insulation and to comply with the relevant U value to be achieved. Because of the type of foam required for roof spaces, the foam will have a slightly wavy surface and vary in actual depth from about 35 mm to about 50 mm. Hence 40 mm is really nominal 40 mm and as an exact depth cannot be sprayed. It is spray applied direct to the underside of the tile or slate. This is sufficient to provide excellent bonding and roof insulation.

Comparing polyurethane foam with mineral wool

Rigid polyurethane foam is about 3 to 4 times more effective than mineral wool or glass wool insulation products so depths do not have to be as great to achieve a more than adequate level of roof insulation. Moreover, polyurethane foam insulation is a roof seal system and prevents cold drafts something that other insulating products do not adequately achieve. As a method of roof insulation polyurethane spray foam is unsurpassed since it needs less depth of material and offers the best price performance and efficiency compared to conventional insulation products with additional benefits of control of air movement by sealing, draft proofing, weather resistant and excellent thermal and sound insulation properties. It is also quick to install and a relatively easy retro fit product.

DIY foam vs. professional rigid foam application

The polyurethane foam rigid roof insulation used by IsoSpray is a class 1 fire retardant, is 95% closed cell formulation and so semi permeable and allows timbers to naturally breath, and inhibits wet and dry rot. It is not a DIY product due to the nature of application (125 and at a pressure of 600psi) and the skill required during application. It bears no resemblance to DIY foam products sold in DIY stores which are low density, provide poorer thermal insulation, are flammable and cause timber sealing which can potentially lead to timber rot. It is a high performance spray foam that insulates and bonds a roof giving an extended roof life of many years, perhaps 100 years or more, and provides a cost effective and quick method for excellent roof insulation and for creating a warm roof to help eliminate condensation.

The appearance of the foam when cured is not meant to be a decorative finish so it is typically used in areas where decoration does not matter, e.g. lofts. Spray foam will be uneven and not smooth or level which is why the trade provide depth of foam in ‘nominal’ depths, around the figure but not guaranteed to be on the figure. Also, a certain amount of overspray is inevitable due to the pressure of application. If something is not meant to be covered with foam near to the area to be sprayed you are advised to mask up before having spray foam installed or pay the contractor to do so.

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