is it ok to build sleeper wall straight onto the ground??

[joboatbuilder]

Hi, I've read several posts on here but can't quite find what info I need, so hopefully someone will read this and be helpful!!

We have a random stone built 1860s cottage with a suspended timber floor in the living room. Many of the boards have rotten (several patch jobs done over the years) and so have the joists, especially where they were simply pushed into the wall. We've had a chemical dpc injected and had boards up for new central heating so had a good look then. What has happened is someone has chocked the joists up on piles of half bricks at random intervals- no mortar or dpm, and the floor is terribly un level and bounces. There is no sleeper wall in the middle, the room measures approx 15' by 13'. The joists run accross the 13' length.

We want to pull it all out and put in new joists and t&g floor boards (which will be varnished), and put in whatever is required to support it all properly, and the correct damp proofing etc.
My questions are:
1. Do I need a sleeper wall to run under the middle of the floor to support the middle of the new joists? Or will new treated timber joists prevent this anyway, as the old ones must be weak and flimsey?
2. What is the best way to support the joist ends at the walls? I was considering building a sleeper wall beside each wall of the house, topped with dpm and wall plate, so that the new joists don't actually come into contact with the (damp) wall of the house. The new injected dpc is at floor level, so would be above the joists
Or can I just screw a timber wall plate to the stone wall, and if so how would I damp proof it??
3. If sleeper walls are the way to do it, is it ok to build these straight onto the ground under the floor - it is just a load of earth and rubble and rubbish. Or do I need some kind of foundation first?

Thanks in advance!!

 

[PaulJR]

Hmmm tricky.

I would go the sleeper wall route. It does need some sort of foundation, but I wouldn't jump in and start digging, unless your cottage has been under pinned at some point it is doubtful that your walls have any foundations either, and you don't want to undermine a wall.

I would be inclined to clean off the area for the sleeper walls to get a firm level (ish) strip of ground and then put 3 or 4 inches of concrete down to give a level starting point. Use engineering bricks for the sleeper wall and put a dpc in the wall at some point. Keep a clear gap between sleeper wall & cottage wall and leave weep holes (gaps in vertical joints) in the first course. Set your wall plate up as you describe. I would recommend that you build a 9" thick wall it will be much stronger than a single skin of bricks.

13' so 4.0m in new money, 8"x2" joists will span that or if you like building walls 4"x2" will work with a central wall. Joist centres at 400mm in both cases.

I wouldn't start adding load to the existing walls in a building of this vintage, tricky at best, and difficult to get a good fixing.

If it was my house I would clear the floor area and cover it with a few inches of concrete, I would also look into fixing insulation under the floor - between joists or such, and you might want to think about ventilating this void - to let it dry up.

 

[joboatbuilder]

That's great thanks very much for the advice.
I'll be going for two sleeper walls and 8x2 joists, don't fancy doing any more brick work than is really required!
You're right about the sub floor ventilation, we've already put a few air bricks in (there was just the one which probably didn't help the rot situation!)
What are the merits of concreting the whole area? Is it just to tidy it all up, or a damp issue?
And another quick couple of questions; roughly how long would I need to leave the concrete to harden before laying the sleeper wall? and similarly how long between laying the wall and laying the joists & floor?

 

[PaulJR]

If you pour your foundation concrete one day you should be fine to lay bricks the following day, same with the walls & the joists.

Oversite concrete. TBH I am not 100% sure, but I think it's just a good idea generally. Stops some damp? but it will stop infestation, ants etc and help stop some moulds?

 

[stuart45]

I would consider building more sleepers. This is the normal way on a ground floor as it saves on timber and you need less earth removed.

 

[str]

if you are going to the trouble of taking out all of the old flooring and joists, why not pour a concrete floor instead?

if its put in right, no need to worry about cross ventilation and no damp through the floor. Better insulation properties than a suspended timber floor, you could even go down the route of underfloor heating if you wished

your new wooden floor can just be laid as a floating floor on top of the concrete sub floor.

 

[joboatbuilder]

That has been suggested to me before. I'm not sure about that solution as far as I can see the issues are that the dining room floor sub ventilation (the room next door) would suffer, we would have to re route the (new) central heating pipes and electrical cables... or would we?

I have not yet compared the material costs of a concrete floor (plus flooring) versus a new suspended floor - anyone got any indications? I still have an open mind on the situation as not going to do it for another month or so... thanks!

 

[stuart45]

You can get round the ventilation problem by putting ducts in the floor.
There are a lot of old cottages where I live that have had concrete floors put in.
However it has been said by a few people that the damp that came through the old floor has now been driven up the walls making them damper.
If you are constructing a new timber floor there are different methods of insulating it to bring it up to modern standards.