Loft Boarding (I'm a bit confused)

[Darnell]

Hi, I've been searching other posts on boarding a loft, which have been very helpful but I'm a bit confused on one or two things... I plan to use some 8'x2' t&g chipboard as the floor (as this seems the cheapest option) and I've got lighting cable running over the joists in the loft so was going to use some 3"x1" batons to raise the boarding. My questions are:-

1. Am I right in thinking that the 3"x1" batons should run at rights angles to the current joists?

2. What direction does the chipboard then go? In the same direction as the ceiling joists or the batons?

3. How far apart should the batons be?

Any help would be very appreciated, thanks.

 

[OLD]

Battens on top of joists ?2x1. flooring at right angles, mark cable runs, and screw fix for maintenance

 

[masona]

1. Am I right in thinking that the 3"x1" batons should run at rights angles to the current joists?

Yes in opposite direction

2. What direction does the chipboard then go? In the same direction as the ceiling joists or the batons?

The way I do it is to put the 3"x1" at 2' centre so the T&G is resting on the 3"x1" centre

3. How far apart should the batons be?

As above

 

[Darnell]

Thanks for the advice guys. Seems like two slightly different ways of laying the battens, but both explanations make sense. I'll just have to buy the wood and get on with it now. Thanks again.

 

[djhowes]

Strikes me that 3x1 at right angles to joists would be 50% more expensive in wood than 2x1 on top of the joists.

Key here is joist spacing. If the existing joists were at 600mm centres then 2x1 on top of joists with 22mm boards at right angles would have all the strength you would need.

If the joists were irregularly spaced (or not 400mm or 600mm), then cross-battening would allow you regularise the support to provide the necessary board edge support. (I understood that it is the board thin ends that must be supported rather than the long sides).

If the battens are just to provide a path for the existing wiring to pass over the joist then battens on top of the joists strikes me as easiest and cheapest. However, if you think you will want to put other services over the joists (water supply, central heating pipes, other electrics), then cross battening will provide you with a usable service run at right angles to the existing joists over the whole floor area.

 

[JohnD]

the cross-battening spreads your weight across several of the original roof timbers while you are clambering about up there, and makes the whole thing more rigid when it is all screwed together.

(it also gives room for cables, and allows you to position at ideal intervals for your chipboard and additional insulation)

 

[morrik27]

So what would be the best option here... 3X1 or 2X1 - or is it just down to cost?

 

[masona]

Doesn't matter, 3"x1" is easier and more supportive where the T&G is resting on the centre of the 3"x1". I wouldn't say it's that more expensive to do.

 

[JohnD]

I used 75mmx37mm because my supplier happened to have vast quantities of it to clear

Not sure how essential it was, but I treated it all with Cuprinol Green before assembly. Much easier to do it the back yard and you can do a more thorough job.

 

[morrik27]

OK, now for a silly Question/Assumption......

You put the 3X1 flat on the joist, running at right angles to the ceiling joists of the loft.....

then have the T&G set so it rests in the middle of the counter baton.

use 400 centres?

 

[morrik27]

oooohhhh........

What thicknes T&G do you reckon??

Am i right in thinking that it's either 19 or 22mm?

 

[JohnD]

position the battens so that there will be one under the ends of the boards, and (assuming they are loft packs about a metre wide) one in the middle.

If you are using 8x2 boards they don't need one in the middle. You won't be using 8x4 boards because they won't go through the hatch. Also consider the spacing of your loft insulation. It will be convenient if a roll fits tightly between the timbers.

You can also use 8x2 ply, if it isn't too expensive locally. 18mm is plenty. Ply is stronger so you could use slightly thinner but then must support the ends. When it is all screwed tightly together it will be much more rigid. It's only for light storage, the loft timbers themselves won't support heavy goods or parties. You can use 12m ply for shelving that you won't walk on e.g in the eaves or on the gables.

The battens and boards aren't "one size is correct and all others are wrong". See what's available convenient and cheap. I can get timbers 2400mm long into my loft; and board 8x2, but you may not be able to.

 

[masona]

You put the 3X1 flat on the joist, running at right angles to the ceiling joists of the loft.....

Yes

then have the T&G set so it rests in the middle of the counter baton.

Yes

use 400 centres?

Whatever the width of the board is

 

[morrik27]

Cheers guys, as always your help and expertise is priceless!

 

[djhowes]

oooohhhh........

What thicknes T&G do you reckon??

Am i right in thinking that it's either 19 or 22mm?

When I boarded out my attic I used Kronospan P5 boards; the Flooring Grade boards are sized at 2400mm x 600mm and come in either 18mm or 22mm thickness. The manufacturer's guidance is clear - 18mm must not be used on joist spacings that exceed 450mm. My joist spacing was 600mm so I had to use the 22mm boards. Note there is a right and a wrong way up for the board; if it's the wrong way up then the T&G joints don't have the correct strength.

There was one unintended advantage of using 22mm boards; by combining the flooring with 15mm plasterboard ceilings, I did not have to install any form of acoustic insulation in the floor space to meet the the building regs. If I had been able to use 18mm boards or had 12.5mm plasterboard then my acoustic insulation costs would have been about £1200!

The edges of the boards have to be supported on all edges except when glued to adjacent T&G board ie around the edge of the room there has to noggings to support the board edge (actually my building control officer said that there had to be a 50mm gap between the nogging and the wall).

Tip: Make sure that the boards have fully actimatised before fixing to the joists; I was amazed by how much the boards had shrunk when dried out (about 75mm over an 8m run). The Kronospan web site advises:

Allow a clear movement gap of 2mm per metre run of floor at each wall and an absolute minimum gap of 12mm at each wall. Gaps should be left around rigid up stands including pipes.