Penetrating damp or just poor practice – thermal imaging answers the question

Penetrating damp or just poor practice – thermal imaging answers the question.

A recent damp survey in York, came from a distressed client who thought they had problems with penetrating damp in the bedroom – so we booked them in for a survey.

The couple live in a north facing two storey semi detached house, constructed under a pitched roof with concrete roof tile covering and external walls constructed from 275mm insulated cavity brickwork built in the 1990’s. The bedroom is situated on the first floor overlooking the front of the property.

Our client highlighted some rather strange looking isolated patches which had begun appearing on the bedroom gable wall fairly recently, which she thought was damp.

Picture taken of the bedroom gable wall, discoloured patches highlighted on the second image by the red circles.

An external inspection of the building revealed no concerns as the property appeared watertight. A series of tests were undertaken on the wall surfaces using a protimeter MMS (Moisture Measurement System)  in both search mode and measurement mode and the results were low indicating the wall and surfaces were dry.

Next step, I turned to thermography for some deeper non disruptive investigation. Using our specialist thermal imaging camera I scanned the walls, and the images reproduced reiterated the above noticeable patches, although something else was apparent? A thermal anomaly, a distinctive change in temperature of the surface extending downward from ceiling level.

The thermal image above shows a temperature variation throughout the wall, with the cooler temperatures represented by the darker colours and the warmer temperatures by yellow- white – note significant change in temperature extending from ceiling level.

To verify my initial findings, I re-inspected the wall surfaces and the results were again low, so I headed up into the roof.

The roof was of truss construction and the ceilings were insulated with 8″ (200mm) of fibreglass insulation. Above the front bedroom there was a noticeable gap between the structural wall, wall finishes and ceiling. I should mention at this point the walls were finished with plasterboard adhered the structural blockwork beneath, a method know as “dot and dab” in the industry.

Unlike other rooms insulation was missing above the front bedroom ceiling adjacent the gable wall, revealing the plasterboard ceiling fell short from the gable blockwork leaving a visible gap directly behind the wall finishes. The issue was not dampness, but cold air intrusion……..

The roof was well ventilated with soffit vents present at the front and rear allowing air to migrate through the roof space for ventilation purposes. Unfortunately however, the gap present at the wall / ceiling junction was allowing cold air to pass within the small cavity between the blockwork and plasterboard. The adhesive in this case acted as a “cold bridge” allowing a change in temperature of the walls surface, where ever the adhesive was present, visible as isolated discoloured patches within the bedroom.

A thermal can of the room also highlighted where cold air was entering the roof through the soffit vents cooling the ceilings perimeter at the eves and where insulation had been disturbed in the front corner.

Air entering the roof through soffit vents at the eves cooling the ceiling perimeter.

Air cooling the ceiling where insulation had been lifted within the roof.

So good news for our client, the building is watertight, but they have a small issue with cold air intrusion which if left unattended could lead to interstitial condensation within the wall/finish cavity and mould growth over the forth coming winter months.

Solution

The solution was a combination of; sealing the wall / ceiling junction with a specialist caulk to prevent cold air entering the cavity, insulating the ceiling along the gable elevation; extending insulation across the eves to prevent cold air intrusion cooling the front perimeter; adding tile vents to re-introduce ventilation within the roof and update the overall level of insulation to meet recommended standards of 12″ (250mm); and a lick of paint to the walls – problem solved.

Insulation companies have a tendency to leave ceiling insulation short of the eves to allow ventilation within the roof to continue. In theory this is correct, however the consequence is cold air entering the roof through the soffits cooling the ceiling perimeter which can create issues with mould along the wall/ceiling junction. One way to counteract this is to extend the ceiling insulation into the eves cutting off the eves vents and thoroughly insulating the ceiling, however you must remember to reintroduce ventilation back into the roof by adding tile vents to prevent a build up of humidity. Remember If installing tile vents within the roof covering ensure the area of low level vents is roughly twice the area of high level vents and never fit ridge vents or high level vents as the only means of ventilation otherwise you will create an updraft, drawing humid air out of the property through the roof.

For more information on condensation within roof see our other post – Improving levels of loft insulation

Regards

Russell Rafton C.S.R.T / A.Inst.SSE
Dryfix Preservation Ltd – Surveyor

“Yorkshires leading damp & timber specialists”

www.dryfix.net