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Attic tidy up, 300mm insulation and flooring

spr1nt3r

Hi all,

I have decided to remove old and patchy insulation from in between the joists (100mm / 4" thick) and replace it with a new batch and cover it all with tongue & groove MDF.

Now the recommended thickness for insulation is around a foot (300mm) which is grand but what's the best way to construct it all? Do I just get 2x8 to add another 8" (200mm) and lie them down perpendicular to existing joists with MDF on top or what's the best here?

Since I am DIYing already, any advise on reducing clutter of horizontal roofing boards (sorry but don't know the name for them) and making it less of a head bash hazard eg. replace them with just a strong / stronger solution that would not be in the way as much?

Any advise is welcome. I'd like to do as much as possible on my own, with your help of course :rolleyes:

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Comments

whizbang

You only need to floor whare you are going to use the space, ie. not up to the edges shown in pics. But having said that, covered insulation works better than uncovered in a draughty attic.

You need qualified structural advise before moving any timbers up there. Remember theres Tons of tiles on top of this flimsy timber.

spr1nt3r

whizbang wrote: »

You only need to floor whare you are going to use the space, ie. not up to the edges shown in pics. But having said that, covered insulation works better than uncovered in a draughty attic.

You need qualified structural advise before moving any timbers up there. Remember theres Tons of tiles on top of this flimsy timber.

Thanks for the reply. The flooring is just so I could store some light boxes so the walkway would be clear really. And as you said covered insulation is probably better.

Any advise for a structural engineer? They seem to be mighty expensive.

fred funk }{

Dont under any circumstances cut away any trusses. They're carefully engineered to support the roof.

Get some attic floor stilts which raises the floor. Don't compact the insulation under as it reduces its effectiveness.

neiphin

You have kings pan insulation in all ready, you won’t improve on that

As for roof, keep away or the lot could cave in on you

sgthighway

Don’t cut any of that timber as you have no Rsj to carry the weight. Your roof could belly or twist in and break any water tight seal you have. Don’t use mdf. Some 2x4 lengths of osb board should do it. I think I see a length in the photo. Attics can be a dumping ground so maybe just sheet of around the opening.
Did you re-slab the ceiling below? It is foil backed which is good.

jack of all

Do not remove any of the longer timbers nailed to the underside of the truss members- that's bracing and gives a trussed roof its stiffness and do not interfere with any of the trusses or timber runners either- they are there for a reason. As already advised use OSB (or ply or flooring grade chipboard) for flooring- MDF will sag over those truss centres and it doesn't respond well to moist air.

sydthebeat

neiphin wrote: »

You have kings pan insulation in all ready, you won’t improve on that

As for roof, keep away or the lot could cave in on you

That's not Kingspan insulation.

That's the foil backed plasterboard of the ceiling.

sydthebeat

The counter battens will allow you to put 150mm deep quilt between the trusses as is. They look 600mm centered so essay enough to do with minimal rolling.

You can then use some 36 x 150 joists perpendicular to the trusses and roll out another layer of 150mm quilt between.

Then floor over whatever space you want for storage

Dr_Colossus

sydthebeat wrote: »

You can then use some 36 x 150 joists perpendicular to the trusses and roll out another layer of 150mm quilt between.

As rare as hen's teeth, tried getting exactly above last year for a similar project. Called a number of places to no avail. McMahons had some listed in Cherry Orchard but when I visited that was a false alarm and they only had 44x150.

Near impossible to get 1 1/2" timber in anything other than 75x35mm from builder providers which is a shame as no need for the extra strength/weight when over-boarding an attic.

sydthebeat

How about using 150 x 22s and bridging @ 1.35 centers.

Slightly more work but same end result

jack of all

When I did something similar in my own attic I was lucky enough to have access to a machine thicknesser so I could reduce timber "cross" joists down to 36mm. However if I was doing it again I'd use something like these:

https://www.screwfix.ie/p/diall-loft-storage-stilts-210mm-12-pack/243gf

Loft stilts or whatever they're named would allow you to cross batten on top with 38x 32 rough sawn battens with flooring on top- a fraction of the weight and work required with using full depth joists and a lot less effort trying to manoeuvre long and heavy lengths of timber around a confined loft. Using these would allow better continuity of the insulation with less thermal bridging through deep timber joist sections.

celticbhoy27

If you're going the insulation roll route, a handy way to cut them to size is to buy a cheap electric carving knife (Argos 15 quid) saw this tip online and its been a game changer. Cuts like knife through butter. Perfectly clean cut too

spr1nt3r

Thanks the lot of you for so many answers and decent advice. This helped me a lot.

I will focus on Loft Stilts aka Loft Legs of some sort to increase the height of the floor by 175 or 200mm and then just board everything with T&G; found KRONOSPAN 18mm 2440x590. It will be a b***c to get all through the opening but I will manage. Doing it only once I hope...

That will give me the recommended insulation plus a bit of storage space. Just need to figure out how to treat the far end of the roof where I clearly won't be able to stuff anything, never mind 200mm extra.
Any advise on that bit please?

Dr_Colossus

spr1nt3r wrote: »

found KRONOSPAN 18mm 2440x590. It will be a b***c to get all through the opening but I will manage. Doing it only once I hope...

Given the fan or W shape of your roof trusses 8' x 2' sheets will be a nightmare to fit as you'll have to cut around multiple uprights especially considering your floor will be that 6-8" higher.
I'd advise to get the smaller loft packs that are 4' x 1', will work out a bit more expensive but save endless amount of heartache
https://www.goodwins.ie/products/OSB-Loft-Pack-1220x300mm-18mm-x-3-1.1M2.html

spr1nt3r

Dr_Colossus wrote: »

Given the fan or W shape of your roof trusses 8' x 2' sheets will be a nightmare to fit as you'll have to cut around multiple uprights especially considering your floor will be that 6-8" higher.
I'd advise to get the smaller loft packs that are 4' x 1', will work out a bit more expensive but save endless amount of heartache
https://www.goodwins.ie/products/OSB-Loft-Pack-1220x300mm-18mm-x-3-1.1M2.html

I was eyeing them yokes alright. Does add around 30% on top of the cost but yeah, would be much easier to work with and I guess I need the same amount of stilts anyway :rolleyes:

policarp

I fixed 2 x 1 treated battens 150 mm. above joist level fixed to the trusses after laying 150 mm. of insulation.
then used flooring boards to deck out the area I wanted.
No need for 6 inch timber.