How to renovate or repair the metal roof with polyurethane spray foam

Last Updated on: 18th March 2021, 09:54 pm

Last Updated on by Viliam

An uninsulated metal roof

Metal roofs and walls in industrial and farm buildings suffer from two major problems that can be solved by spraying with polyurethane spray foam, thermal heat loss, and condensation.

An uninsulated metal roof will suffer from very poor thermal insulation and this leads to not only a very cold building in winter, and very hot in summer, but also to condensation. This has been traditionally been solved by insulation batts typically made from fiberglass or glass mineral wool insulation or branded products.

How to lay insulation batts

The insulation batts are simply placed edge to edge and so do not form a continuous barrier since the gaps allow airflow and thermal leakage. Also, the insulation material is not “closed” and in fact, air can move from one side to the other albeit slowed down by the insulation bat. Insulation bats also require a vapor barrier but because of the depth of insulation required and the necessity of an air gap, there is more than sufficient air within the structure for convection air currents to form and cause condensation.

The batts cannot be placed directly against the underside of the metal roof skin without condensation ruining the insulation material by water absorption which is an excellent thermal transmitter and thus renders the insulation bat totally useless. This has been solved by allowing up to a 150 mm air gap on the underside of the metal roof and allowing for cross ventilation which contributes to further thermal heat loss but almost stops the condensation! The very nature of the insulation product means that it adds to build costs and times but does not totally solve thermal insulation or condensation problems in metal roofs and metal cladding.

Polyurethane foam – a better metal roof insulation solution

What offers a better metal roof insulation solution? Polyurethane foam both stops condensation and insulates. The spray foam will spray seal any gaps. It is applied directly to the underside of the metal roof skin but can also be applied to the top metal roof skin where an existing roof needs to be both fully renovated and insulated. The depth of spray foam applied governs the ‘U’ thermal value but even a minimum depth of just 25 mm will stop condensation.

The method of metal roof renovation and repair is to spray foam (the foam is a special dense noncompressible foam that can take light foot traffic) on the top skin and then apply a 2 part continuous skin that seals the foam. When the roof has to be both renovated and insulated this is a very cost-effective solution.

On a typical metal roof to achieve a U-value (W/m2K) of 0.25 using traditional insulation bats typically requires a bat depth of 200 mm and even more. With polyurethane spray foam the depth needed is less than half of that and has the benefit that it is applied directly to to the metal roof skin.

Condensation control and thermal heat loss problems are solved cost-effectively using polyurethane spray foam.