Is The Kitchen Too Hot Chef?

Some years ago I was on site to advise why the stepped and staggered gable abutments between houses were suffering dampness. Indeed, the problem was so widespread in excess of fifty households had complained. It would be inappropriate to name the company responsible for the site of over 200 units but it is known nationally.

Henry was the name of the person overseeing the design and specification of work of the developer. He explained the gable abutments had been constructed incorporating traditional roll dpc and a stepped running lead flashing. He went on to add that the houses had been constructed to the usual design detail and specification used on all their houses built throughout the UK. Why then were the gables on this particular site damp?

One of the immediate answers was staring us in the face. This site was exposed, and by exposed I mean built off steeply rising ground facing seaward. The area was known to be both wet and gusty in the winter months. I asked many questions, making notes as the answers were received. I then asked the obvious: ‘ If this site has been constructed to your usual specification, have you or are you experiencing problems elsewhere?’ Following some hesitation the response was unbelievable:

‘Well, yes we do have other sites with similar problems, but not affecting as many units as we have on this one….and generally our specification functions. It’s only when properties come under pressure with bad weather that the gables leak – otherwise they’re OK’.

I thought about this last sentence. It took some believing. ‘It’s only when properties come under pressure with really bad weather that the gables leak – otherwise they’re OK’.

I had a mental picture of a trading standards officer chastising the company for not being more truthful with its advertising. But perhaps it is difficult to sell new homes as being ‘ watertight as long as the weather is not too bad’?

My mind raced to what might happen if Henry decided on a career change and became an aircraft pilot? Would he announce the plane would crash only if bad weather was encountered?

Perhaps he might instead become a chef? Food poisoning occurs only if the kitchen is under pressure?

We inspected fifteen of the units. Masonry had been removed and it was clear the dpc and flashing arrangement was inadequate. I suspected it functioned to an extent that minimised water ingress but could not arrest it and prevent it permeating inwardly. In most situations the ingress went unnoticed affecting the masonry within the attic space only. But in exposed situations the dampness permeated further.  Thus it was no longer out of sight – out of mind? The dpc lacked a watertight inboard upstand and the shape of the dpc varied from one course to the next. The stepped running lead flashing had been introduced in 1.8 metre lengths, but the tuck-ins failed to always unite with the dpc. Of course, being a running flashing it lacked any overlap or secondary layering. Therefore any wind-driven rain that blew under the stepped leading edge was in immediate contact with the very masonry that was supposed to be kept dry.

For a stepped or staggered gable abutment to be protected against rain permeating and descending below the roofline (where it becomes an internal skin of the abutting property), any damp protection system must follow the pitch of the roof. The arrangement resembles the profile of a staircase – with connecting treads and connecting risers.

This protection must then link with an appropriate flashing to weatherproof the physical join between masonry and roof finish. By so doing the requirements of the Building Regulations can be satisfied.

(Picture right – typical stepped abutments correctly executed)

The developer in question decided to insert preformed trays into the gable masonry and the exercise eliminated all the damp penetration problems. The tray inserted was the Type X cavitray with attached lead flashing manufactured by Cavity Trays of Yeovil. (The Type X has Local Authority Building Control National Type Approval). Since using the Type X cavitray for corrective purposes and subsequent new build applications, there has been a dramatic fall in maintenance costs as damp penetration of gable walls no longer features in the snagging list.

The Type X is just one of the products awarded European Technical Approval, and Cavity Trays Ltd is the only tray manufacturer in Europe awarded this commendable standard. Cavity Trays is also alone in supplying cavitrays with a product performance liability warranty – of particular attraction to Architects, Builders and Clients who appreciate and value peace of mind.

When it comes to gable abutments, Henry is now exceedingly well informed. And if you are preparing to fly away on holiday or eat out tonight, do relax. Henry is still employed by the developer!

Eight hours after it stopped raining, dampness is evident in the gable masonry of this typical development. (This is not the development referred to in this article).

Once saturation point is reached, cement-based reconstructed stone of this style can discharge into the cavity in excess of two litres of water per sq metre per hour.

The Type X cavitray with its own attached lead flashing solved all the gable damp penetration problems on the site. The self-adjusting and self-supporting cavity upstand permits the tray to fit all popular cavity widths. Compatibility is thus ensured.

An extract from the Cavity Trays Ltd survey into damp problems

affecting sloping abutments in the UK.

The pie chart provides an analysis of faults. The programme of investigations is ongoing and Cavity Trays Ltd regularly issues updated data. Please refer to Cavity Trays Ltd publications for the latest information.