How to board an insulated loft?

[abenn]

The other day a council pest controller said he was unable to go into my loft because it's not boarded. Aware that other trades (TV aerial, electrical, plumbing) might take the same view in the future, I'd like to put down at least a longitudinal walkway so that access can be easily gained to the far end.

But our loft has had top-up insulation, in accordance with "official" guidelines, which means that the joists all have a thick layer of insulation matting on top of them. So what is the proper way to lay a strip of boarding, please?

Do I cut a 2ft-wide (or whatever) strip out of the top layer of insulation so that I can simply screw the boarding straight onto the joinsts, and then lay the cut out insulation strips back loosely. Or do I put timber blocks onto the joists to raise the boards so they pass over all the insulation?

 

[studips]

when i upped my insulation, i put 6x2" timbers on edge, pinned them to the joists with screws then boarded over that to give a raised deck and full insulation. if it's just a narrow walkway you could board over the existing joists & replace the insulation with something of a higher performance and so have a thinner layer

 

[PrenticeBoyofDerry]

Simplist and most practical way.
Is to remove(for time being) or place out of way the extra layer(s) of insulation above your current ceiling/loft joists.
Then run extra timber joists over the top of the existing joists, to get a full depth of 270mm (the recommended level). So if your current joists are say 170mm add new timbers that are 100mm deep.
The timbers are best layed perpendicular (at right angles) to your existing joists.
Space the new joists out at 400mm centres, this will give you a good solid structure to board on to and when installing 2400 loft panel/floorboards this will reduce the number of cuts needed.
Then once you have installed you raised timber joists, you can then fill the void back with the insulation.
Always start your boarding out from the loft hatch and the jobs a good one.
One word of warning, if you have any electric cables, such as shower or power socket circuits within the void where the insulation will be layed, prevent these from being totaly surround by insulation. They are ideally best clipped direct to timber joist and above the insulation level.
Lighting circuits on 5A or 6A fuses/mcbs/rcbos are generally okay, as it is normal to have these wired in 1.00 or 1.5mm cable, which can carry the current safely, even after derating factors.
If you need anymore advice, please reply with your questions/queries.

 

[abenn]

Thanks for the responses.

I like the idea of 4x2 (or whatever gives me the right height) at right angles to the main joists. Seems to me like I could just cut slots in the insulation where the new joists are to sit, without having to shift anything out of the way.

Then, which board to use? I see on B&Q's web site, for instance, that they do chipboard flooring in 2400x600x18mm sheets, and "loft panels" 1220x325x18mm at roughly the same price per square metre. Loft panels are presumably favourite, for they're easier to manhandle through the hatch.

So, for a 600 wide walkway running the length of my loft (i.e. across the present joists) I should install three parallel lengths of 4x2, at 325 centres, to support the centre and two edges of two panels of boarding laid side by side? Given that it's only for occasional use, is there any need to support the joins at the ends of the boards?

 

[PrenticeBoyofDerry]

I personally would lay the panels the other way around still keeping your joist centres around the 405-10mm mark. This will allow you to have more insulation within the void and save on the cost of additional timbers.
You have no need to support the edges of the panels as the tongue and grove edge, once clipped in will offer additional support to those.
It is also worth while staggering the panels/boards as you would with laminate flooring or plasterboard ceilings.
Here is a link, it's a ceiling but will give you the impression/image, I am trying to but across. It's the first diagram on the PDF
http://www.zurich.co.uk/NR/rdonlyre...DE0F7CFBC0/0/PlasterboardCeiling107782A02.pdf

 

[abenn]

Thanks, PrenticeBoyofDerry. I don't understand how turning the panels round would allow me to have more insulation within the void, since the idea of the 4x2s is to raise the panels above all the insulation.

I'm only trying to create a walkway, not board the whole loft. So using loft panels I'm figuring on two panels wide, or maybe three at the most. I take your point about staggering joints though.

 

[PrenticeBoyofDerry]

I am assuming that you are not only raising the floor level, you are also insulating between to new voids created, as that is the whole point of doing this.
So assuming this what your intending to do, this is how it works.
You will have more insulation, as you will have about 375mm space between joist to fill with insulation.
If you centre your joists at 325mm as you wish to,
then you would be insulating void of 325mm rather than that of 375mm.
If we work this out per loft panel @325x1225mm and your extra 100mm depth.
Taking in to account the joists width and the regularity of the spacings.
You will get approx 3.5 cubic metres of extra insulation per loft panel.
Plus there should be a reduction in the linear metres of timber you would be using.
With it being only a small area the cost savings on the timber may not be that great but you will get more insulation within in the voids, after all you already have the insulation there.
It is totally up to you, like I said personally this is the way I would go.
The practicalities, costing and the time consumed fitting extra joists. I would sway with my method. Even more so, if you were to board out the whole loft floor.

 

[abenn]

I am assuming that you are not only raising the floor level, you are also insulating between to new voids created, as that is the whole point of doing this. ...

No, I've already got the extra insulation, above all the original joists and insulation. My point is simply to provide a safe walkway over it, partly because tradesmen won't go in the loft now without boarding, and partly because if you do go in the loft you can't see the joists so you don't know where to put your feet

 

[PrenticeBoyofDerry]

I understand that you are trying to make it a safe working area for tradesmen and yourself.
And you are insulating between the raised joists, but using the insulation that is already existing, as it is currently over laying your joists.

Like I have already mentioned the recommended level of insulation(rock wool, mineral wool etc...) is 270mm.
The method I have described, if you decide to use it? Will supply you with better insulation properties and should keep the material cost and the labour times down and most importantly of all, does the trick.
But again the options are yours, I am only trying to offer you the method I would personally use and also used by others. As in most cases it is the most logical, practical and economical method of doing this.

 

[abenn]

Our house came with insulation between the joists, up to the tops of the joists. Last year we had extra insulation added, which was simply laid over the top of what was there, and the joists. I don't know what the overall thickness is, but it was installed under a British Gas promotion, supposedly in accordance with current guidelines, so I'm not thinking to add any more.

So, yes, I simply need to raise the joists enough so that the boarded walkway will clear the new level of insulation.

 

[PrenticeBoyofDerry]

So, yes, I simply need to raise the joists enough so that the boarded walkway will clear the new level of insulation.

I have given you all the info needed to do this, in the above posts.
Good luck with your project.

 

[misterhelpful]

Don't want to tread on toes, but I think this is being over-complicated.
If it were me, I would notch out the insulation as you have already stated. As you only want a 600mm walkway, I would run two perpendicular joists at 600mm outside edges and another in the centre for extra support. You could fit the outer joists at 600mm centres which would give you scope for joining further boards at a later date.
With these spacings, you would be better served using the 2400mm boards as they can then be layed lengthways along the new joists (600mm outer edges)and can be cut in half/thirds to make them easier to get through the hatch.
Obviously, boarding out wider areas/entire loft would mean fitting the flooring perpendicular to the new joists.

 

[abenn]

I have given you all the info needed to do this, in the above posts.
Good luck with your project.

Yes, thanks, PrenticeBoyofDerry. I think we're all on the same wavelength, thanks.

I'll figure out the detail, whether it's best to use 600mm wide boards or two 325 wide loft panels, after I've measured and done some planning. I prefer 2400x600, but the loft panels will be easier to handle.