Building a level floor over a sloping garage floor ...

[LeeElms]

My workshop is in a double garage with a floor which slopes front to back, with the difference in height from front to back being a couple of inches.

I think I recall there was a post a year of two back about someone that had laid an insulated wooden floor over a sloping concrete one, but I can't find it.

Can anyone help to find it ?

 

[RogerS]

Was it this one?

Entered 'concrete' and 'sloping' into search, select 'search for all terms' and 'posts'...

 

[LeeElms]

Thanks for the suggestion, but that's not the one I recall. The one I recall was much more like my situation, of an existing, concrete floor with a few inches of slope (over about 5m).

I've tried all the combinations of 'sloping', 'floor' etc. I can think of ...

 

[RogerS]

This one?

 

[LeeElms]

Thanks, but it isn't that one.

The one I recall (I'm pretty sure it was on this ('UK Workshop') forum) talked about cutting tapering 'joists' to provide a support for sheet covering (plywood / OSB or similar). That's the detail I'm interesting in. The existing floor is quite smooth, but sloping (it's about 3" in 5m, just measured it).

 

[stairman]

Have drawn what I think you want here. You can either pack standard thickness timber to height or cut larger timber down

If the floor only slopes one way place the timber across the level direction

 

[LeeElms]

That's an interesting approach -- in that the post I'm trying to locate used the approach of cutting tapering joists along the direction of the slope. I was hoping the post would tell me an easy way to do that.

Can anyone suggest what spacing I would need between such 'joists', if I were going to use OSB (18mm ?) as the flooring material ? What options for fixing / cross-connecting them do I have. I don't want to make a mess of the concrete, as I guess this floor would need removing if we sold the house and the new owner actually wanted to use the garage for a car ...

 

[Anonymous]

Hi Lee

The tapered "joists" are firring piece's similar to what are used on flat roof's to allow water to run off. You could use them, but a lot depends on the flatness or lack of it on your concrete. It may look smooth but is extremmely unlikely to be a perfect flat plane especially if its anything like the conctete finishing in my garage :lol: (NOT my work) So cutting identical firring piece's will very likely result in an uneven deck surface, and cutting each piece seperately is possible but fiddly. What I would do is fix 2 joists to the walls with rawlbolts/resin fixings whatever you prefer, and use a laser or water level to get them both absolutely level and on the same plane. Then use string lines from side to side and set the other floor joists onto small pier's using mortar and little brick offcut's or slate packing piece's so that the joist's upper surface's are level with the 2 joists fixed to the walls. Add a DPM between pier's and underside of joists and your away. Get 50 mm foam cut to fit between joists, nail or screw T&G chipboard.
Hope this helps

 

[Keith Smith]

I use a laser to check the floor level, or out of level, as garage floors are rarely flat in any plane. Stairman's method is the easiest, just plane up each batten to thickness.Tanalised battens are the best bet just make sure you are careful and wear a decent respirator.

If you want to cut battens with a taper I usually mark them up and cut them on the bandsaw.

The battens don't need to be so accurate, a couple of mm out won't make any difference.

You will need to lay a vapour barrier over the battens and any insulation, otherwise you'll get moisture forming on the cold concrete; and I'd use 22mm t&g chipboard rather than OSB, makes a much better floor. After all that's what it's designed for :wink:

 

[RogerS]

Lee

I'd go with Mr Spanton's approach. Keiths' approach is also viable but seems to me to need a lot more work...planing/tapering each piece.

I have used these packing pieces and my prefrred approach is to rip several different thicknesses of timber to suit the floor as it tapers down. Then using the string method suggested by mr S, pack up with the shims. Much better than faffing around with mortar.

 

[LeeElms]

Thanks again for all the contributions.

What about a recommendation for the spacing between the timbers ? Do I need to interconnect them ? (The heaviest items I have in the workshop are TS2500CI TS and HMS260CI PT).

 

[Anonymous]

Much better than faffing around with mortar.

Your right Roger it would be a faff on. I thought possibly folding wedges but then they need to be fixed, as they can split and move etc. The screwfix ones seem a decent solution as they will not split or rot either. Only thing is wont you have to do drilled fixing's through joist and wedges (or very close to the wedge's) to hold the joist's firm against the floor and to stop the wedge's moving about when the floor flexe's about in use? Either way thered be "scars" if Lee was to remove the floor prior to re-sale. Several holes from frame fixings (or whatever else you used to fix the wedge/joist arrangement) or remnants of mortar. If I did use mortar I'd make a weak mix that would chip off the existing concrete easily. To do it, all youd need is lay mortar in say 3 or 4 lines across ways depending on the joist run, add say a slate piece, dpm, then rest the joists on this and tap down until they are level with the strings on the 2 fixed ones?? Swings and roundabouts. I used the folding wedge and frame fixing method to alter a floating floor (adrift on 50mm of foam) to have 50x50 battons under to take ceramic tile's in the kitchen and toilet, as the foam had sunk in places (near the doors esprecially) and the subfloor was those pre cast concrete girder's (which were all over the place as level as my **** :roll: :lol: :lol: So the folding wedges came in useful for that sceanrio.
Cheers Jonathan

Ps I once saw a superbly done solution to the problem of sagging joists in an ancient French house. The owner scribe fit packing pieces to the exact curve of the joist, but level on the top's, and all the tops in the exact same level plane. (Something had to be done as there was about a 2 inch deflection in the centre's, and he didnt want to strip and re floor with new joists and the joists were sound apart from about 400 years worth of sagging). It might sound naff, but actually it looked bloody good as he used clean new oak or chestnut which contrassted nicely with the old dark oak joist's and it looked sort of contempory, modern also. Didnt try to hide it shows evidence of its own making etc :lol:

 

[LeeElms]

Any guidance on the separation of the joists, please ? And do I need anything spacing / joining these joists ?

 

[PowerTool]

Normal joist spacing is 400mm centres.Span of joists is related to joist size (e.g. an 8"x2" can span a greater unsupported width than a 6"x2")
Given the fact you are intending putting this over an existing concrete floor,there is nothing to stop you putting supports mid-span (or more often,if you prefer) - verticals from the concrete floor to the joist to stop any possible sag/bounce.

Andrew

 

[OLD]

Thats a 1 in 65 slope is it worth the expense of levelling you could consider making a level assembly area say a dais in timber and shim up any large benches and machines if it was required.
If you need a wood floor then dpc and floating flooring chip board (glued up) on top of the smooth concreate you keep the floor strength

 

[Shultzy]

LeeElms - Firstly I would check the level of the concrete floor and determine the how much out of level it is. If the out of level <= 1/4" don't bother with packing pieces. If > 1/4" use mr spanton method of packing the joists.

Get your local wood supplier to cut firings from "difference in slope" + 1/2" to 1/2" for length of garage, less 3" to allow for the covering material to find the floor. Space them at 16" centres and cover with 3/4" to 1" material of your choice. Lay DPC under joists and insulate if required.

 

[Anonymous]

Well I got to thinking about this scenario, and I think there is an easy way to do it without using mortar/ screwed fixing's into the floor etc.

I'd still use 2 wall plate's attached to the walls either side, but taper them to allow for the 3 inch drop (seems like a hell of a slope but maybe the garage is extra long as well as wide?. So they would be 4 inch deep at the down end and 1 inch deep at the up end. This gives room for at least some insulation at the thin end and also something to fix the deck to, with minimum loss of ceiling height. So if the garage is say 19 foot long, I'd get a 19 foot 5x2 (I would have to scarf 2 together probably to get the length and mark out so as to get 2 firring pieces from the one scarfed board). Then rawlbolt them to the opposite wall's, use a water level or lazer to ensure they are absolutely level along their length and also across ways to each other, they should be resting on the floor (with a dpm under). Then I'd obtain the width between the taper'd wall plates, the walls are unlikely to be spot on parallel. Cut 4x2 joists to length, then drop the first one in on a dpm resting on the concrete, and skew nail it to the wall plates. Then keep working up hill at 400 mm centres, drop the joist in, mark off for height from the 2 wall plates, join the 2 marks with a chalk line, rip off with circular saw, drop in onto dpm, skew nail to plate's etc etc. If theres excessive crowning or valleying in the concrete you might need a tempoary wedge to stop the joist rocking as you mark the heights off the 2 wall plate's. As you travel uphill the offcut's get wider and you can use them on the thinner levels towards the top. I wouldnt bother with strutting (herringbone would be too deep anyway) as the joists are resting on the floor and nailed at their ends so they arent going to be able to deflect too much, and as OLD sudgested a 22 mm t&g deck will stiffen everything up nicely anyway
The only scarring would be the rawlbolt hole's in the wall which you could easily repair with a spot of mortar. Mind you I do think is it really worth the hassle, especially if it alters levels for doors etc?
Just another thought, hope it helps :lol:

 

[LeeElms]

Thanks again for all these ideas. It will take a bit of thinking as to which is most appropriate for me.

The other problem of course if what to do with the machinery in the workshop while doing this work ... it sounds like more than a days work to me, even with as much pre-preparation as possible ...