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Conservatory Construction – protection against damp at intersection

Author/Issuer: Cavity Tray Standards    Added:

Subject: conservatory construction / applicable building regulations
Protection against damp penetration
Roof / wall intersections

To Be or Not To Be?
That is the Question

A solicitor acting on behalf of his client in a building dispute recently quoted the words of Shakespeare. The client considered work carried out by a builder to be unsatisfactory and had instructed his solicitor to seek damages.

The building project was very simple and straightforward. It consisted of a large new conservatory, which was added to the rear external elevation of a brick-built house. The house had cavity walls, the actual cavity being 75mm with an inside skin of insulation block. A laminated floor was laid in the conservatory and it soon became an integral part of home living. For the first four months all was well.

Then winter came. The original outside wall of the house (now inside the conservatory) started to become damp. One day the laminated timber floor was discovered to be awash, and it subsequently swelled and ballooned.

The solicitor asked for what purpose the conservatory was erected – and this proved the crux of the matter. If the conservatory was intended as a living space, it was subject to certain building regulations. Had the proposed use of the conservatory been made clear? A living space – to be or not to be, that was indeed the question.

The insertion of cavity trays could have prevented the occurrence that caused so much damage. Ironically it transpired the builder had actually recommended his client have trays fitted when the project was negotiated, but the client had declined on the basis they added cost to his project! He settled for the conservatory to be flashed only, failing to appreciate penetrating water can by-pass a flashing.

If one looks to the NHBC, it has wisely stipulated conservatories attached to NHBC new homes should be protected with cavity trays. This is excellent discipline and defines exactly what is necessary and what is acceptable. Unfortunately the position with most existing dwellings is not clear-cut. One often witnesses ridiculous attempts to weatherproof roof/wall intersections with flashings only, aluminium tape and occasionally large quantities of mastic!

With the current emphasis and encouragement of television programmes for homeowners to use conservatories as an extension of their living space, there are undoubtedly going to be more and more homeowners who discover the hard way that dampness does not discriminate, and will continue to gravitate in a wall that is still exposed externally.  Unless a cavitray is introduced to alter the status and behaviour of the original property wall, it will be problematic.

And what of the solicitor’s client? He was advised his initial thriftiness was his decision – and the resultant problems therefore of his own making. The cost of replacing the floor, introducing trays, and making good internal decorations cost many times more than the cost of the trays he originally declined!

Most architects, surveyors and builders will recommend installing trays, even if the initial use proposed of a conservatory is uncertain.


Published within Learning Curve, Master Builder.

Suggested reading: Type E and Type X cavity trays by Cavity Trays of Yeovil.


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