Cavity wall gap is only 1 inch

MiserlyMartin

Hello.
Recently had some new windows and doors put in and I was looking at the cavity while the windows were out and was shocked at how small the cavity was! I measured it. It varied due to uneven external brick lengths and bits of cement that look like they are breaching the cavity (see picture) but it was only a 1 inch gap. There is no cavity wall insulation just a membrane inside as you can see hopefully.

Is this cavity actually performing any function due to its small size? And will it be suitable or worth having cavity wall insulation fitted? Could it cause damp and have no effect?

Any advice from any building expert would be wonderful, thanks.

David_Aldred

Hi - what you are looking at is the cavity return where the inner leaf of wall is returned to the outer leaf at openings. In modern construction there is often a vertical damp proof course that may include insulation to prevent cold bridging at the return where the inner and outer skins of the cavity wall meet. The cavity width to the main part of the wall may be wider and worth checking by carefully drilling or removing a sample brick if you are concerned. Kindest regards, David

27col

Actually David, the picture seems to be on its side and there is a vertical damp course, as you suggest, which can be seen if you study the picture. I suspect that the cavity is probably the correct width. The gap that the OP measured is probably due to badly fitted cavity closers. Your suggestion about removing a brick to measure the cavity is not really necessary as the cavity can be worked out by measuring the overall thickness of the wall at the opening.

MiserlyMartin

Hi thanks for the replies. Yes that is a view of the side of the window. I did measure it as I say only an inch, but you think thats ok?

Is it suitable to have cavity wall insulation fitted then?

eco-friendly_2

It's only an inch around the openings! time to get your survey done.

tonycamps

Your cavity wall needs to be aminimum 50 mm wide for insualstion. There are a few companies that may be prepared to risk less however I do not reccommend. If a void is created it allows warm air to be trapped circulated and this in turn can create damp

27col

I would still like to know what is the overall thickness of your wall, from the outside to the inside. Once you know that it is easy to find out the width of the cavity. If you are measuring the rough looking gaps as shown in the picture, that is not the cavity that you are measuring. Those jagged bricks are the cavity closers and should bridge the cavity right up to the vertical dpc seen in the picture.

MiserlyMartin

I measured the overall thickness of the wall, it is 27cm. Hows that looking?

KeithP

MiserlyMartin wrote: »

I measured the overall thickness of the wall, it is 27cm. Hows that looking?

So that's 10cm-ish for the outer brick, 10cm-ish for the inner block, 1.5cm-ish for the plaster... leaving 5.5cm-ish for the cavity.

How's that looking?

MiserlyMartin

Its looking like 55mm ish then! So I need to get a survey done? From whom? I am a bit suspicious of a lot of these companies that offer cavity wall insulation in the local press. They talk about a grant etc, but do not mention any technical details about the type of insulation filling used or its thermal properties etc. I worry one of those companies would say the walls are ok to fill just to get the work - then I get a damp house¬!

David_Aldred

Hello Martin & 27 Col,
Obviously the picture is on its side and equally obviously one may see the dpc material in place. Referring to my previous post above I was making a comment that in modern construction a vertical dpc may include insulation (which this photograph shows a dpc without such insulation) to prevent cold bridging so apologies if this implied that I could not see the dpc in the photo.

Whilst the width of the cavity within a wall may be suspected to be a distance by measuring the window reveal that is certainly not a confirmation of cavity width or its condition.

Martin with regard to having a survey of your property to determine if it is appropriate for cavity wall insulation you may as you indicate ask a company selling such for profit to advise you whether such is appropriate (and be aware that there are several different types of insulation material that all perform differently).

However if you are of the view that to consider asking a company selling a product whether that product is actually appropriate to be installed in your particular property may not be the impartial qualified opinion you require from which to make an informed decision upon the matter (and be aware removal if it is not will both be highly disruptive and expensive); then you may wish to have a qualified independent specialist survey undertaken to provide that impartial advice and results of such investigations.

Such surveys may be undertaken by Freelance or Consulatant surveyors of the Property Care Assocation (PCA) a list of which may be found by looking upon the PCA website and selecting find a member and then selecting Freelance or Consultant to have a chat with a couple of such specialist surveyors in your area regarding the matter. Their inspection should include photographic or video inspection of inside the cavity wall for you to view at a later date, a report on the condition of the cavity wall ties, any bridging of the cavity, the type of brickwork and mortar etc all within a detailed report and investigation of any dampness within the property all of which may have a bearing upon the matter.

Kindest regards, David Aldred CSRT, MIWSc, CSSW, AInstSSE, Independent dampness, cavity wall and timber surveyor.