Property Remedial Articles - Olympic Construction

Earlier this month, I received instruction to undertake a pre-mortgage survey for dampness, the instruction was not specific or relating to any particular area of the building.

The property was a standard end terraced property with a small out rigger to the rear, which was used as a kitchen, the weather was dry, but the external air was temperature was -1*c

On arrival at the property, my first impressions where that it appeared to have been well maintained from the outside, it looked as if the roof had been recovered , and new PVC gutters, soffits and facia boards had been fitted.

As with any type of inspection, I always start with a visual inspection first, which allows me to note any areas which may require a more detailed inspection. It became obvious from the start there was a condensation problem within the kitchen of the property, as there were a number of areas affected by black mould Aspergilius nigar  to the walls and particularly the kitchen ceiling.

Mainly from a point of interest I used the Protimeter MS2 to measure the relative humidity within the various rooms of the property, along with the surface temperatures at the time, these are noted in the table below.

As can be seen from the readings the internal air temperatures within the property were quite high, so the air would be capable of holding a high level of moisture.

Air temp…..21*c                RH ……………53%

Dp 11.5*c                           Wall surface 15*c

The inspection of the damp proof course found no issues, there wasn’t really any more evidence of condensation in the form of mould to the remainder of the property, apart from some small issues to the window reveals.

So my attention was drawn back to the reason why the kitchen ceiling was so badly affected by mould.

There were no defects to the external of the roof to indicate any form of water ingress, I was informed the roof had been recovered in the last six months, with new felt and external PVC cladding systems installed. But one point which did stand out, there was no ventilation installed to the roof covering or PVC cladding system of the roof.

I mentioned this to the property owner, who was following me through every step of the inspection, only to be informed, that no  ventilation was required, as  ‘ breathable roof felt’ had been installed which was required by building regulations.

There was a roof trap located in the kitchen ceiling so the next obvious step was to take a look in the   roof void. The ceiling was constructed of standard 12.5mm plasterboard, insulated with 100mm of rockwool insulation, along with a number of stored boxes and right enough, breathable roof felt had been installed. But what was clearly visible was the heavy layer of condensation which had formed on the underside of the breathable felt.

There was clearly an issue here with condensation forming within this roof area, my first thought was the contractor had installed the felt the wrong way up, so trapping the moisture in the roof void, but this was not the case. Using the MS2 I took relative humidity readings from within the roof void which proved, what was already evident, the underside of the roof was below the dew point temperature and condensation was readily forming on the underside of the felt.

Conclusions The problem here was due to a combination of issues which when combined resulted in the condensation forming.

condensation loft
The lack of a moisture vapour membrane being installed at the kitchen ceiling level. This could have easily been installed by using ‘Duplex plaster boards’ which has a foil backing preventing the movement of moisture vapour into the roof void. The installation of roof ventilation is still required to be installed into the roof covering and sofits, even with breathable felt being installed, as the felt on its own is insufficient at allowing moisture vapour to escape, as can be clearly seen from the evidence within these photographs.

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