bay window underpinning

[plasticpigeon]

The builders who vandalised my house, had a go at rebuilding the brick base to the bay window. It was pretty much falling over as a load of roots from gorse bushes were growing through it, so needed to be done. However it has been built in a very unsightly way so I am planning to do it again. They also had a go at underpinning it by throwing some concrete down a pit below the wall. This has been done in a very slap dash way, in fact only really underpinning the front half of the wall. However the concrete level is too high as it is about level with the ground and I don't want to see the concrete and wanted to put some bedding plants in the and can't. i am definitely going to dig the concrete out next year, but should I fill the void left with compacted soil and build off that as per original construction, or do a proper concrete pour, that offers support to the whole wall? (the wall had foundations of only 2 bricks deep).

 

[DJH]

Hmm They did you no favours there Plastic. I would do what you plan to do, dig up the concrete, take out what you have under the inside skin of the wall (keeping it propped up somehow) pour in concrete to a level about three courses below the existing bricks and then build up with something like an engineering brick (they will not be seen as the earth will cover them) and take the opportunity to put in a dpc. Well, that's what I would do....

Doug

PS If you have a problem propping up the wall do the concrete in two pours, stick some reinforce bars in the first pour so that they will tie in with the next pour.

 

[stuart45]

I wouldn't use compacted earth as you won't get it firm enough for a decent foundation. There will always be some movement in it.
It is quite a common job to underpin bays on old houses as the builders often put in a shallow foundation compared to the house walls.
You often see the bays on Victorian houses leaning out.

 

[plasticpigeon]

That 's what happened on mine, the wall was leaning out and the roots from bushes grew straight through the foundations. They were only 2 courses deep. I hoped maybe earth would be enough, it would make my life easier, but it looks like i'll have to pour some concrete.

 

[stuart45]

Before concrete was used, the bricklayers used to spread the footings. ie. Start the bottom course on the ground say 18 inches thick, next course 13.5 inches, and then the 9 inch work on top.

 

[MdB]

Definite no to back fill + build on top.

I would dig out to undisturbed ground then fill with concrete to a suitable depth (*). You don't need to fill to the top. Use foundation blocks on top of that to bring the height up to the point where you want to start your wall. I would also build the wall to modern spec with DPC, cavity, tray, insulation etc. unless there is a very good reason not to.


(*) Building control are the people to ask what is suitable - it depends on your ground conditions.

 

[Lime]

Why dig out the concrete?
What's done is done.
Remove the top layer of concrete protruding into the garden in V slices with an angle grinder until a reasonable amount of soil can be put in place to support plants.

 

[middi]

Apart from roots digging into the bay window wall there may also be another reason why these bay window walls tend to give up prematurely over their lifetime. One of the most common problem is that the original foundations were never dug to the same spec as the rest of the building in the mistaken belief that as there is little load and stress on a bay window base wall it would remain stable same as the actual building foundations. Well, that maybe not always the case.
The baywindow wall foundations , if not dug at similar depth of actual building walls will react differently as far as any differential in movement, therefore ( usually) becoming detached from the rest of the building.

If you want to go the trouble of starting all over again regarding the bay window wall, i would suggest to consider what I have noted above.

Middi