Mr Roofer

It seems this is the season when condensation rules. We have received a record number of enquiries this winter from customers plagued with condensation problems.

A developer in Romford had built new apartment units in the autumn and had followed the architect’s designs throughout. The roof called for powder coated steel sheets and the insulation in this building was designed to be installed at loft ceiling level to meet the building regulations for U value. All well and good, plans passed etc. The buildings had been erected in the autumn and new owners had started to move in during December and January.

The first the developer knew that there was a problem was when one of the very first owners to move in complained of water staining on his new ceiling in the bedroom about 3 weeks after moving in. A week later another new owner complained of staining on the ceiling and then another. One could be isolated, two could be a coincidence but three water staining complaints is definitely a trend! On inspection it was found that the fibre wool insulation was completely sodden, totally wet through. At first a roof leak was suspected but it became apparent that the roof was watertight and that the real cause of all the damp was condensation.

Condensation is caused when water vapour within the air meets a surface at lower temperature and reduces the average energy of the water vapour within the air such that condensation occurs. On a steel sheet which has high conductivity, the steel will drag the air temperature down sufficiently where air meets the steel sheets such that any water vapour within the air condenses out.

So, with a large steel roof a major design fault had been incorporated within the building despite the loft area seemingly being adequately ventilated. The ventilation was never going to be sufficient to cope with the speed that the large expanse of steel was sucking the warmth out of the air. As air temperature drops the ability of water to remain vapour is reduced and it will condensate out typically first on the coldest surface, in our case the steel roof. As the average air temperature dropped near the steel roof water droplets formed and dripped off the steel into the mineral wool insulation below. The mineral wool acted as a sponge and transmitted the water down into the ceiling boards. Where after some time the ceiling plaster board sucks in the wet and stains appear on the underside.

So we know what the problem is and what is causing the condensation problem but what is the solution? Well the problem was easily remedied by providing an anti-condensation coating of polyurethane spray foam. The foam was sprayed at 120 degrees and 600 psi to ensure an excellent bonding with the steel. Polyurethane is such an excellent insulator that air and steel within the loft the steel are separated and the foam presents a “warm” surface and so water vapour will not condense on it. We also recommended that the steel joists used in the roof construction were similarly coated since they will produce sufficient cold bridging to cause condensation to form on them. Our advice was accepted.

And the water staining on the plasterboard? Well no easy solution other than take down all the boards and put new ceilings up. Once plasterboard gets soaked the boards looses strength and will eventually bow and possible drop down, not something a new home owner would be prepared to tolerate on a new house.