Timber Garage Floor Construction ?

[jedmc571]

Hello,

My Garage is 17' long it has a gradient about 3' out from the kitchen door, and runs off to the up and over.

I pulled a string line and level, from what I think will be finish floor height to the up and over, and it measures 135mm to the concrete.

Is this easy enought to do in timber? I wouldn't do it in concrete in case we sell in the future rendering the Garage useless as their's a 5" step at the opening.

I was considering going wall to wall ( 7' ) at 400mm centres with pressure treated joists, but my issue is how to tackle the slope and how best to fix to the concrete?
Everything after the first joist would need to be cut at an angle almost like firring strips, and then about 10' back towards the kitchen door it would be slithers of timber just shimming up?

Not sure what to put on top either? 22mm MR T&G Chipboard, or ply? I intend to cover with rubber matting after.

Any ideas

Smells like a Mike Garnham question to me :wink:

Cheers

Jed

 

[MikeG.]

Who, me?

 

[Karl]

Hello,

My Garage is 17' long it has a gradient about 3' out from the kitchen door, and runs off to the up and over.

3' :shock:

Or do you mean 3 inches :lol:

PM me your address - i've got a good book article on installing a false workshop floor.

Cheers

Karl

Edit - i've got your address.

 

[MikeG.]

Jed,

spanning 7 feet in timber is very easy: 6x2's at 400 centres will do it under normal loads........with the point loads associated with heavy machinery you might want to go to 7" or 8".

I don't quite follow your measurements. You say there is a 3 foot fall, but you also say that at the garage door there is only a 135mm difference between level and the top of conc.

If it really is 3 feet, then I would be bolting a girding beam to the walls each side, and using hangers off those to suspend the joists.

If it is 135 at worst-case, then again, I would use beams along the walls, but packed off the concrete. Using beams along the walls not only supports the edges of the sheet material, but more importantly means you will end up with a level floor without hours of faffing around.

As for flooring material, 'twere it me I would use T&G plywood, at least 20mm thick. I would also suggest you take the oppotunity to insulate between the joists, and that you keep the void ventilated.......which may mean inserting some airbricks in the garage walls.

Whatever you do, make the void inaccessible to insects and vermin. There would be nothing worse than having rats move in to that lovely warm dry home you built for them!

Mike

 

[OLD]

Your post is difficult to understand a picture may help, my interpretation is you have a 17 foot concrete floor with a estimated 1 in 40 fall so you could just live with the fall. Or lay strip dpc and firings 17 feet long (wood yards will cut them) screwed to the floor then moisture resistant chipboard t&g floor over.
If you do not level then visqueen over floor and chip board on that.

 

[crazylilting]

I don't quite follow your post but I have a concrete floor in my shop i may want to get rid of because it was poured so badly in many batches that it is all over the place and also has a mechanics pit that is boarded over.

I was thinking of jack hammering the floor out completely, then compacting some dirt gravel mix followed by a vapour barrier. Then taking a laser level marking the outside walls for Joist hights that will later be bolted to the walls with enough air space bellow for ventilation. However i'm putting in an HRV unit for ventilation. I don't want rats or insects at all.

Then kingspan insulation in-between the joists and a 3/4 inch plywood floor. tong and groove if i can find it. I haven't don the span tables yet to determine the dimensions of lumber, but my project is a year off, so not to worried.

The main thing is solid. dry, insulated and well ventilated as mike suggests. As my floor will be at grade level drainage and damp-proofing are also important. Something you might want to consider as well if you are attaching the joists to the outside walls.

Edit: After rereading Mike's post I'll be upgrading the plywood, didn't know you could get thicker in this country. You can get up to one inch in Canada but it is pricey so i imagine the same would be here as well.

 

[jedmc571]

Sorry Guy's I knew this would be difficult to explain

Ok....

1.We're standing at the kitchen door looking out towards the Up and Over

2.The full length is 17 feet

3. The first 3 feet is relatively flat, it then starts sloping down towards the Up and Over

4.I pulled my string line from the kitchen door to the up and over, and when it's level, the distance from the line down to the concrete is 135mm ( at the up and over end )

5. The width is 7 feet

6. So using 6 x 2 the first one would need an inch cut off the depth and have to correspond with the slope on the floor, all the others would need the same doing until I reached the 3 feet point from the kitchen door, and then it's probably some form of shimming

7. So if the kitchen door end was Zero by the time we reach the up and over the total slope is 135mm

I hope this make sense :wink:


Old,

Your suggestion was the first way I considered, but they would need a lot of fettling to get them to match the slope, like I mentioned its almost Zero to 135mm and I wouldn't be able to translate that at the yard

With regards to insulation, with a max depth of 135mm at one end only I don't have much room for it, is it essential ?
The garage is 12 years old, very dry, fully insulated with 50mm Quinntherm and 18mm OSB 3 over the top, the boiler is out there and so warm, I was just going to put DPC on the bottom of the joists?

Hope all this has made it a little clearer

Jed

 

[9fingers]

JED, I think I would aim to rest lateral joists on the concrete with each joist being different height to take out the slope.

Do some sums but if you bought 6x2 stock and started at the up & over door end ripping progressively wider strips off, the off cuts could get used at the far end.

I've done a floor in my house like this with little more than tiling batten sized strips in some places. After all it will be in compression onto the concrete.

PS we must be on the same wavelength as I understood your first description

Bob

 

[jedmc571]

Cheers Bob :lol:

How did you go about fixing to the concrete ?

The kitchen end I was going to gripfill, as they wil be around 10mm I imagine, but when I get to the other end I'm not sure what to do?

As it's so dry, do I need Pressure Treated ?

Cheers

Jed

 

[9fingers]

I did not bother with fixing other than wedging against the walls and inserting some offcuts as noggins to preserve the spacing. Once you get the plywood deck on it wont move around.

Your floor might be dry now with good airflow and a boiler in the garage but this might not be the case when the airflow is cut off.
I would lay a heavy polythene DPC and for what little extra it costs, I'd use treated timber but this would not be vital.

Bob

 

[MikeG.]

I did not bother with fixing other than wedging against the walls and inserting some offcuts as noggins to preserve the spacing. Once you get the plywood deck on it wont move around.

I would lay a heavy polythene DPC and for what little extra it costs, I'd use treated timber but this would not be vital.
Bob

Sorry to disagree with you Bob....

Fix this floor down properly, Jed. This is your own floor, and there is no reason at all not to do the job properly. If a job is worth doing, its worth doing well.........You would not be happy to find that wedges shrank and fell out, and part of your floor flexed a little.

Bob is right about the DPM (I presume he means M, not C), but do make sure that this doesn't interfere with the airflow.

Treated timber without hesitation. Don't even think about uising untreated......you'd be crazy.

In addition to the design I gave you previously, use solid blocking at the halfway point of the joists. You'll be amazed how much stiffer this makes the floor. As I said, don't just use joists.......run a beam along the walls as well.

Mike

 

[OLD]

From your reply treat the first 3 feet as direct lay on concrete and have the firings made to 14 feet to level the rest it keeps it simple and inexpensive.
One 14 foot 6x2 will give two firings re treat cut edges.

 

[9fingers]

I did not bother with fixing other than wedging against the walls and inserting some offcuts as noggins to preserve the spacing. Once you get the plywood deck on it wont move around.

I would lay a heavy polythene DPC and for what little extra it costs, I'd use treated timber but this would not be vital.
Bob

Sorry to disagree with you Bob....

Fix this floor down properly, Jed. This is your own floor, and there is no reason at all not to do the job properly. If a job is worth doing, its worth doing well.........You would not be happy to find that wedges shrank and fell out, and part of your floor flexed a little.

Bob is right about the DPM (I presume he means M, not C), but do make sure that this doesn't interfere with the airflow.

Treated timber without hesitation. Don't even think about uising untreated......you'd be crazy.

In addition to the design I gave you previously, use solid blocking at the halfway point of the joists. You'll be amazed how much stiffer this makes the floor. As I said, don't just use joists.......run a beam along the walls as well.

Mike

No problem Mike. I based my comments on my lounge floor laid 20 years ago and I'm currently sitting on it (via a chair!) as I type and no hint of bounce or movement. Your method would be more sturdy - no argument there.

Bob

 

[jedmc571]

OK I'm getting the picture now.

Mike, are you saying lay a DPM sheet on the concrete first then joists over the top ?

Can I not put 100m DPM stapled on the bottom of each joist ?

How do I get a fixing through a 5" joist into the concrete ?

What fixings should I use ?

Who wants to do it for me :lol:

Sorry for all the question

 

[misterfish]

OK I'm getting the picture now.

Mike, are you saying lay a DPM sheet on the concrete first then joists over the top ?

Can I not put 100m DPM stapled on the bottom of each joist ?

How do I get a fixing through a 5" joist into the concrete ?

What fixings should I use ?

When I did my workshop floor I used the belt and braces approach. First a proper poly DPM on the concrete. Then I used pressure treated 3x2 joists. As I had a couple of rolls of 100mm DPC I also put a layer of this beneath the joists. I then fixed the joists to the concrete using frame fixings that I had. In your case I'd use a spade bit to make a deep countersink hole and then use ordinary and masonary bits (in an SDS drill) to go through the rest of the wood and into the concrete. Also I used noggins between the joists and extra bits around where the table saw is plonked. I ran wiring to the TS, filled the spaces with rockwool and coovered the whole with MR chipboard T&G flooring.

I still get the odd creak from the floor in a couple of places but it works well and the floor is not cold on the feet. To make it more comfortable I also have interlocking foam tiles that make standing for a long time fairly comfortable.

Misterfish

 

[jedmc571]

Thanks misterfish

That's pretty much how I'm doing it.

I bought 8 6 x 2 s and 8 sheets of 22mm MR Chipboard, I did try and get T&G Ply as Mike G suggested but they only had 18mm or 25 mm and the 25 was big money!
I did underestimate how many joists I would need as well :roll: they only had 2.4m or 3.6, so I got the 3.6 so I had offcuts to make noggins.

The chipboard is wrapped up in a Tarp in the garden, and so I got stuck in cutting the joists, that's when I found out I needed more, I was quite angry, but I'm no expert, and my wife said, "If you were good enough to calculate and install it right first time with no problems, you would do it for a living, you don't, so stop beating yourself up " I took some solace from that
So they're all cut to size, with 2 scribed down each wall ( is that a rim beam ? ) but not fixed so I can double check I'm ok before doing so, and at the moment I'm not

A few more questions if I may ?

1, I have started with a full 6" depth at the up and over, and as I work backwards each joist needs a little taking off, should I bother trying to cut the corresponding angle off the slope and shim any undulations, ar just cut them square and then shim up ?

2. When inserting packers/wedges I was planning to put some polyurethane glue on them and then fit them,so the glue would expand taking out any gaps, and keping them there if they shrink etc ( I hope my thinkings right ) and then any other gaps, I was going to run a bead of expanding foam both sides.
The gaps I have a very small, just from the ones I dry fitted today their was more shimming to make them plumb, than to take up gaps, the floor is quite level left to right.

3. On an 8' run how many noggins would be suitable, I tried 2, it looked a little weak, but 3 seemed ok, but I have plenty of ofcuts to make more, so I'm open to suggestion.

4. How the bloody **** do I get photo's onto the Forum

Many thanks

Jed

 

[9fingers]

Sounds good so far Jed.

Don't forget to plan out any joints you will have in the chipboard and ensure either a joist or noggin is underneath.

Instructions for photo posting are on the General chat board top line.

Bob

 

[jedmc571]

Cheers Bob,

I'm getting on with it, might have some pic's up later

Jed