Building on top of a single storey extension....any practical experience?

[icravecheese]

We have a lovely, detached Victorian house which we really don't want to move from.
At the moment we have 3 beds upstairs plus a bathroom, we also have a single storey side extension (was once the garage as our neighbour still has her side garage). The side extension currently has a downstairs toilet (which we are soon to make into a shower room) plus a large room we use as a playroom. It has a pitched roof, and is only single skin.

We have 3 kids (all under 6yrs old at mo) eventually all 3 will want their own bedrooms. Plus we ideally want to retain some sort of playroom (now) / teenage living room (in 8yrs or so) so whilst we could use playroom as 4th bedroom, we don't really want to.

Our loft height isnt high enough for a straight forward conversion - would need a roof raise, which is do-able but expensive.

So I wondered how feasible is it to build on top of the single storey side extension? The new upstairs room could be accessed by making a corridor upstairs that would take some space from the currently large middle bedroom.

How much might it cost, plus would it require loads of extra work? Anybody done this??

If it is single skin it probably isn't structurally strong enough to take a second storey (and the foundations will probably be very shallow too). I would guess that you are looking at demolition and rebuilding .

Im looking at this scenario too.

My issue is that the 'garage' part is built on a concrete slab, so doesnt have foundations to support another storey.

Watching thread with interest!

Ah, x posts!

I agree if it's single skin the foundations will likely be too shallow, sorry.

You probably could strengthen the foundations but as you'd need to sort out the single skin issue too, it's easier to knock it all down and start from scratch.

The extension was done about 15years ago, so not sure if builder would've been made to dig deep foundations incase it was going to be turned into 2 storey (I know they sometimes stipulate this as part of planning)....but yes, the single skin bit has always concerned me. Oh bum!

Assuming (big assumption I know!) foundations are ok, could they just strengthen the existing storey to build on top?

You will need to look at the footings first by digging a trial hole. Chances are, they won't be adequate for an extension.

we had a double garage at the side and wanted to build on top of it. It was marginal whether the foundations would be ok so we took the decision to demolish and start a fresh. we were able to prevent the break through into the main part of the house until we were water tight.

we had garage (double length/single width) which previous owner had converted to room and garage. we are currently building over it (only half width due to planning conditions) (and rear double storey extension). We are converting to garage/utility room/family space (next to new kitchen). We had to demolish existing build (apart from single wall which is party wall with next doors garage). New foundations (done in stages to prevent next doors garage falling down!!) and rebuild with new double thickness walls etc.