How do I terminate a cavity wall in an existing window opening?

[TylerDurdenk]

Perhaps a bit of a strange question, but let me try and make sense.

We are planning to extend our small front hall with an extension. Currently the entire front of the house is an opening with a huge lintel that was poured in situ. So we do not have any walls to tie the extension to, only an opening.

Please see a photo to hopefully make sense of it.



The idea is to remove the 4 smaller windows (2 either side of the door), cut the window frame, build the walls, then temporarily remove the big windows in order to fix the frame to the new wall, and then refit the big windows.
This does mean that the ends of the wall will terminate under the lintel and inside the house. So we can use some cavity end caps, or bricks in their ends before plastering and decorating.
Does that make sense?

Do I need anything to secure the new cavity wall to the lintel?

 

[TylerDurdenk]

Another potential problem is the existing floor of the wimdow opening. It's at damp course level and appears to be only one brick thick. The lintel is 30cm thick, but the floor only 100mm thick. What can I do there? Can I lay the new brick wall onto the floorboards?

 

[^woody^]

Bond the cavity ends across each other, or build the two separate and tied with cavity ties and gob the cavity up with expanding foam or insulation before plasterboarding.

I don't understand the relevance/concern of the wall only being one brick thick (or is it 1/2 brick thick?), as it's an internal wall.

Perhaps posting some sort of plan may help us understand

 

[TylerDurdenk]

Thanks for your response.
Here's a plan

Essentially, I am am concerned as the new wall needs to be built all the way under the existing 300mm lintel (minus plasterboard and dab depth), however doing so means I will be building onto the floorboards as the existing outside wall (beneath the window opening) is only one brick thick.

 

[freddiemercurystwin]

Wouldn't you just build it as a cavity wall?



Though you may need to make the return deeper as it looks like you'll end up with barely a 1 brick wide wall for the outer skin.

 

[TylerDurdenk]

Sorry, my plan isn't altogether accurate. The white sections are meant to represent the window frames. They are only 70mm deep.

 

[^woody^]

You can corbel (step) the first course of blocks out 100mm over the floorboards,as long as there is 220mm or so on that wall.

An alternative would be to build that new extrnal wall 100mm in to fix the frames to, and then put in a vDPC and build the inner part of the pier in timber

 

[TylerDurdenk]

You can corbel (step) the first course of blocks out 100mm over the floorboards,as long as there is 220mm or so on that wall.

I don't quite follow this. Sorry.

 

[^woody^]

On your plan, mark out in red or something the thickness of the existing wall you plan to build off. It looks like you have drawn what you want to build, not what is there already.

 

[TylerDurdenk]

Does that help?

 

[TylerDurdenk]

The red lines show an idea of where the brick wall beneath the existing windows come to.

 

[^woody^]

Timber stud internal wall built off noggins in the floor - not off the floorboards. Fill the inside will insulation.

I can't imaging that the existing wall is only 1/2 a brick thick, so at the back is a corbelled block pier instead.

FMT's idea above is OK if you have a wall to build off and the piers aren't too thin. Otherwise they can be flimsy and liable to crack

 

[TylerDurdenk]

Thanks very much for your efforts. I've just had a little explore under the floor boards and discovered an inner wall. Does that change things?

 

[^woody^]

Yeah, you've got something to build off