How to close cavity after windows and doors have been fitted

plywood / osb fixed to blockwork

Do not paint the concrete blocks.

,Agnes

This cavity should have been closed with “L” blocks, which are built in to the inner leaf. See photo.

Here are some details from Homebond House Building Manual.

Your detail is fine.

The Airtight membrane can be fitted over the insulation.

The plasterboard slab reveal can be fixed mechanically to the concrete block and plastered with a 3 mm plaster skim.

The windows and door frames must be fitted with the outer face of the frame in line with the inner face (back) of the outer concrete block leaf.

dathi

The Homebond House Building Manual 7 th Edition was printed in 2012 see photo.

It is the current edition.

It was printed 10 years ago. The 8th edition is coming soon.

The House Building Manual is given by CIF to all Building Contractors.

It’s best to ascertain actual Facts and not make the facts up, and give persons on the forum false information.

The details given in the photos from the Manual are excellent details.

I would not all a Building Contractor to use the detail that you put up, as there is no concrete block cavity closer shown.

Your detail is not in accordance with Homebonds details.

I will let you in on a little secret not divulge by Google - the purpose of the Cavity Closer concrete block is to provide a perfect secure fixing for all external door frames.

In your detail (please don’t mention Cold Bridge and / or Thermal Bridge) would allow the plaster on the internal reveal crack at the frame, every time the external door is allowed to slam closed.

Very mature. As I said before you need to grow up.

For a man who on another thread recently was arguing over the extortionately high prices you charge for engineering being down to the value of your time and quality of your work, to then refer to an engineering handbook first published 30 years ago and the latest update being over 10 years old is laughable and shows exactly what’s wrong in the building profession these days.

OP, or anyone else reading this thread, under no circumstances should you ever allow a shoddy block layer, or engineer, instruct you to use L blocks. When it comes to air tightness and cold bridging it’s the worst of all the options for detailing around windows and hasn’t been done in over 20 years. It is nowhere near meeting the standards required for Part L regulations.

Concrete blocks are the most porous material used in construction and under no circumstances should a concrete block be allowed “bridge” from the outside to the inside or you will have damp spots forming on your inside walls in a very short period after the house is sealed, if you could go so far as to call it sealed with them being used.

I’d be very worried for any of your clients C.Eastwood if this is the type of out of date advice you’re giving to them. I hope if you have houses currently under construction, where this detailing can still be changed, that you’re man enough to now go to the owners/builders and admit to your mistake and get them changed before windows are fitted.

I have been reading the discussion since we are building ourselves at the moment, interesting to read. I checked our drawings and thermal L blocks (e.g. Quinnlite or similar) are specified to close most of the cavity and with the final 100mm closed with a section of insulation.

Thanks, I edited my post as I only had a quick look at first but on closer inspection I can see that they don't close the cavity fully as you said. It's a 250mm cavity and the L looks to be closing 150mm of that with the final 100mm closed with rigid insulation.

There is no need to go above a 200mm cavity in this country as the climate doesn't warrant it. As for using Quinnlite blocks around windows an doors, waste of money. If a cost benefit analysis is done then it is plain to see the savings in heat loss would mean it could take 100 years to recoup the extra cost. Just return the standard blocks to 100mm from the outside leaf and close the rest with PIR insulation. This way you have no thermal bridging, plenty of block to strap the windows to and the airtightness tape can be plastered over right up to the window frame. Proprietary cavity closers are very difficult to deal with when it comes to airtightness.

I would not be taking instructions from Masons.

Adding on a piece of a concrete block to make an ‘L’ block will result in mortar droppings in the cavity which cannot be removed.

This is the reason for using ‘L’ blocks.

I would not allow any mason to use this old fashion method

The mason/ builder saved money by not purchasing the ‘L’ blocks.

See photo.

The piece of 50 x 50 timber in the photo where the cavity between the outer leaf and the ‘L’ block is closed with insulation is a temporary door frame.

There is no cold bridge.