Dodgy extension???

tabbycat1979

I have had a survey done on a house I want to purchase. It has highlighted that the extension (which is the kitchen and bathroom, ground floor) is 100mm thick rendered masonry. I have been told verbally that it is also dry lined but it's not in the written report. The extension is roughly 30 years old, if not more and the current owners have not had any damp problems. Also the extension render coating bridges the damp proof course but I don't understand this!

Our mortgage company has refused to mortgage the house because they think the extension is not structurely sound and that it could fall down in a strong wind! The survey doesn't seem to imply this but may be I'm misunderstanding the above points?

Are there any builders out there that could give me a better understanding of this. Obviously it's difficult without seeing the actual house! But I want to determine whether we are likely to have problems with it in the future and if not, try and find another mortgage lender.

Is it worth the risk?

David_Aldred

Hi Tabbycat,
The function of a habitable wall is to be structurally sound and along with being to a reasonable thermal efficiency at time of construction be able to resist wind driven rain penetration. Many older houses were solid walls and in order to achieve these requirements the wall was thick and uneconomic to build.

Building a cavity wall is an improvement which is where you have an inner leaf of masonry, a void (hence the name cavity) then an outer leaf of masonry all held together with ties here and thereto give it the structural integrity over its height.

This type of wall means the outer leaf of the wall can get wet and the inner leaf should stay dry. The construction has been modified somewhat over the years in the way it is tied and insulated but cavity wall construction remains the norm for the majority of domestic housing stock in the UK.

From the above you can see that if you only have a half brick wide wall equal to only the outer leaf of the cavity wall it is not going to hold back wind driven rain penetration to the internal surface, it is going to be cold / suffer condensation and it will be structural unstable over a certain height.

Such half brick thick walls are often used for single storey outbuildings and are not meant for habitable areas. Sometimes folk try to make the best of things and rather than knocking the outbuilding down will try and convert it by lining the walls internally with waterproof barriers and insulation. Other times dodgy builders wanting to do things without Building Regulation Approval and on the cheap will throw up such extensions with half brick thick walls.

Again from the above you will hopefully appreciate what you are facing and why those who have looked at the property have raised concerns.

Kindest regards David Aldred Independent damp and timber surveyor