Attic flooring question

Benster · 16-01-2008 11:43pm #1

Hi folks, I'm planning to floor the attic in the next few weeks and thought I'd run the plan past you lot to make sure I'm not going to completely muck it up...

The purpose of the floor is to gain some storage space, it's not for active use or actually living on, so it doesn't have to be the strongest floor ever.
It's truss roof and there's already a layer of fibreglass insulation between the trusses. I want to raise the level of the floor so as not to compress this, so I was going to use 1.5" x 4" (poss. 5" if I can get it) planks, then floor over with 3/4" chipboard sheets. The trusses are 1.5" wide.

Q. - I'm planning on running the new planks on top of the existing trusses, in the same direction, not perpendicular. I thought it would be easier to join the two pieces of wood with small plates screwed to both of them. If perpendicular laying is better, how to secure them to the trusses? I don't want to have to screw all the way down through the uppermost plank.

I'm also thinking of not using the T+G flooring packs you see in the shops, because I want to be able to lift individual sheets if access to the ceiling below is required. Is this sound?

Thanks for any advice you might have...

B.

Big Lar · 16-01-2008 11:54pm

To be honest i think that you would be better off to run 3 X 2's on edge accross the ceiling joists at 16" centre's and screwing them into place to avoid hammering and cracking the ceiling underneath, Just remember to stagger the joints.

Then i would go with the tounged and grooved chipboard or OSB flooring on top of that by screwing them down again, the tounge and groove will provide extra support for the ceiling joists as they will spread the weight accross the floor.

If you are worried about access afterwards its only a matter of cutting a hole through them with a jigsaw and making it good afterwards.

Also you might find that you will have to move some cables running through your attic, be carefull not to notch out or drill any holes in the trusses as they are not designed for this.

Lar.

Mellor · 17-01-2008 10:27am

Perpendicular running is far better, you don't have to screw down right from to top, can screw in from the side at an angle.
As for flooring, I wouldn't use T+G flooring packs either. 18mm OSB is perfect.
But I don't agree with Big Lars suggestion that T+G OSB sheets will help spread the load. Sheets will, but have T+G on the sheets won't make much difference,

Benster · 17-01-2008 5:26pm

Cheers lads.

Still sticking with non-T&G sheets, I don't want holes all over the place if I can avoid it.
As for perpendicular planks, this will compress the insulation for sure, so I'm still not sure about that. If I use 2"x4" planks would that leave enough clearance for laying another layer of fibreglass perpendicular also, on top of what is already there?

B.

Aeneas · 21-01-2008 4:29pm

I have been looking into the question of insulating and flooring an attic. For some time I was running with the idea of putting down extruded polystyrene (called Space Board) over my existing fibreglass but the manufacturer (Knauf) does not appear to be willing to confirm in writing that I will not have a problem with condensation. It is also expensive. (Some of this is discussed on another thread). So it's back to the idea of batons and fibreglass as discussed above. At the moment I have 6in of fibreglass between the joists. I am thinking of
1. installing 4x2in planks 16ins apart, at right angles to the joists
2. to reduce the load on the ceiling I would fix 2in shoes, called Speedy Hangers, to the walls at either end into which I would slot the planks thus transferring some of the load onto the gable and interior walls (the attic is 15ft wide between the gable and the wall)
3. I would screw down through the baton where it crosses at right angles the joists underneath
4. place rolls of 6in fibreglass between the batons
5. screw t&g flooring chipboard to the batons.
My two concerns are weight - which I hope will be allievated by the speedy hangers - and compressing slightly the fibreglass by using 4in instead of 6in planks. This might reduce the u-value a bit. Crown Loft Roll 40 has an R-Value of 3.75 at 150mm thickness. So a double layer would give a total u-value of 0.13. Even allowing for some compression I reckon this will give me a value close to the Building Regulations and is as good as I am likely go get with this approach. Grateful for any comments or suggestions?

Aeneas · 27-01-2008 2:06pm

Benster, if you haven't done the job yet you may be interested in my experience. It took me a few days, working intermittently, to floor and insulate an attic roughly 16ft by 16ft. In the end I used 5in x 2in planks for the joists and laid them at right angles to the existing joists, 16ins apart. I went with 5in because I thought 4in would compress the fibreglass too much. To spread the load I screwed 2in metal "speedy hangers" to the walls into which I fitted the 5in planks. This also had the advantage of holding the planks upright while I screwed them at an angle into the joists below for greater stability. I filled the spaces with 6in fibreglass and floored over this with 2 ft wide T&G chipboard bought in 8ft lengths from a builder's supplier. A few tips
- make sure your working area is well lit. This job can't be done with a torch.
- make sure you can get the planks and chipboards up through your attic opening before you buy. Because of my roof design I had to cut the chipboard to 6ft lengths, and divide half the 16ft planks - and then reconnect them with bolts - because they could not be manipulated through the roof trusses in the centre of the attic.
-be careful about electric wiring. Some of mine were slack enough to lift above the planks but others were tight and difficult. In places I had to cut small grooves in the joists below and holes in the chipboard to accommodate them
-use small lengths of chipboard, like the ones found in DIY stores, as temporary flooring while you are working. At least two lengths, one to stand on and one to move. A third is useful for tools.
-it would be a good idea to wear knee pads while doing the flooring and a mask while cutting and fitting the fibreglass
-it would also be a good idea to have a good back. Mine is in bits after all the twisting and turning in confined spaces! But my room below is warmer.

Abraham · 27-01-2008 4:22pm

Aeneas
Very sound advice there which I can agree with 100% based on personal experience.
If you do not do this job right, Benster, from the begiinning, I can assure you that you will have loads of spinoff jobs causing probs for you down the lion. Cracks in the ceiling below, electrical probs, insulation etc. It can become a nightmare so do it right first time is my considered advice.
Best of luck with it.

Zorba · 27-01-2008 11:48pm

I was planning on putting down a few tongue and groove boards in my attic 6 to be exact for an extra bit of storage, but i was just gonna put them down over the existing insulation and compress it down a bit to get the boards on. After reading this thread i'm wondering am i doing the right thing or should i be raising the trusses a bit ?

ttm · 28-01-2008 12:28am

Zorba wrote: »

I was planning on putting down a few tongue and groove boards in my attic 6 to be exact for an extra bit of storage, but i was just gonna put them down over the existing insulation and compress it down a bit to get the boards on. After reading this thread i'm wondering am i doing the right thing or should i be raising the trusses a bit ?

Why? Is compressing the insulation a bit going to push a hole in the ceiling below or cause enough condensation so that the joists are going to rot in 6 months time? I'm a bit OTT on ventilation but the one place I have never seen condensation or mold problems is in or around otherwise dry (ie roof doesn't leak) ceiling. Obviously be sensible about the weight you put on your T n G boards but unless the ceiling is substandard I can't see what damage you could do. But do beware any cables or pipes running over or through the joists as they are often hidden by the insulation, you don't want to trap a cable or put a nail into a pipe. If you are only putting 6 boards down it sounds like you won't even be standing on them and you'll be just stood on a ladder to put things in the roof so I doubt weight will be a problem. btw don't stack ice in the roof in cardboard boxes- its very heavy and attracts polar bears:cool:

Aeneas · 28-01-2008 12:22pm

Zorba wrote: »

I was planning on putting down a few tongue and groove boards in my attic 6 to be exact for an extra bit of storage, but i was just gonna put them down over the existing insulation and compress it down a bit to get the boards on. After reading this thread i'm wondering am i doing the right thing or should i be raising the trusses a bit ?

I put in the extra joists only because I was adding 6in of insulation on top of the 6ins of fibreglasss between the existing joists. If I were simply flooring over the existing joists I would not worry about compressing the insulation a bit, say by an inch or so. You lose a little of the insulation value, but condensation is not a problem. ttm has never seen condensation in an attic ceiling. I have. Where the installers of the fibreglass incorrectly pushed it across the vents in the eaves. I agree with what ttm says about wires and pipes. Use screws, not nails, to avoid cracking your ceiling.

Zorba · 29-01-2008 10:50am

Well i was wondering why others were putting in extra room before fitting the floor boards and was thinking i probably don't need to, to thanks for confirming lads.

Benster · 19-02-2008 12:14am

Well folks, after much grunting and swearing, she's done.

It's getting a bit late, but I have some photos of the progress and final result. To recap:
- I got a load of 5x2 planks (actually turned out 5x1.75) and 8'x4' plywood
- laid them perpendicular across the existing trusses
- fixed them with right-angle brackets (a mix of L-shaped 1.5" and 2" due to shortage of 1.5"s - mix made no difference)
- filled between the new uprights with 100mm fibreglass (existing f/g still rose to 1/2 height of new upright - didn't want to pack it too tight and the 100mm did just right in the end)
- boarded over uprights with plywood cut to fit through hatch.

1. What I started with:

2. Uprights going in:

(the right-angle brackets used)

3. Boards going down over insulation (didn't get any shots of the insulation going down, it was so quick):

4. Finished job:
Here you can see where each board is cut around the vertical trusses

As a complete beginner to this size of a job, it was pretty hard going, backbreaking evenings in the freezing cold

The hardest part was the initial moving around and positioning the uprights. The amount of obstacles up there (trusses etc) made it a complete pain in the ar$e, but once they were down, I put down a couple of loose boards and used them as a movable floor. I actually cut the first plywood boards to fit around the hatch before I had it insulated as this gave me a stable area to work in and leave the tools in.
Aeneas's info is pretty much spot on regards getting a mask and kneepads (I didn't get the pads and now wish I had). DO NOT do this without a mask, I left it off one night and had a bad night of coughing afterwards, that f/g is a killer.

Ok, that's it. Hopefully this will show folk what can be done in this situation. It wasn't an impossible job, I just took it one step at a time.

Cheers,

B.

Wabby69 · 10-05-2012 10:22pm

This is a very well documented project Benster

I hope you don't mind, but I have sent you a PM with a few questions as I am about to embark upon this same task.

Regards

sirpsycho · 19-09-2014 10:54am

Sorry for digging up an old thread but have a couple of questions. I'm intending on flooring my attic over the next month or two.

Is plywood the most recommended to go for? (I assume once chip-wood gets wet it's useless).

When flooring over cables, should I just cut notches in the floorboards to accommodate the cables? Or do most people cut notches into the joists (would that not weaken the joists?)

Where two boards are meeting on top of a joist - is there any need to add extra support like a metal bracket underneath the boards?

Thanks in advance.

dodzy · 19-09-2014 12:18pm

sirpsycho wrote: »

Sorry for digging up an old thread but have a couple of questions. I'm intending on flooring my attic over the next month or two.

1. Is plywood the most recommended to go for? (I assume once chip-wood gets wet it's useless).

2. When flooring over cables, should I just cut notches in the floorboards to accommodate the cables? Or do most people cut notches into the joists (would that not weaken the joists?)

3. Where two boards are meeting on top of a joist - is there any need to add extra support like a metal bracket underneath the boards?

Thanks in advance.

1. Yes, cheapest decent option
2. Notch the boards, not the joists
3. No. Measure and cut properly and you will have no "floating" boards

Attic flooring question

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