Flooring attic

wolfyboy555

Hi I am looking to attempt to floor a bit of my attic in a new build house I have. It's a rather large attic (roughly 60sqm) which is suitable to convert into two habitable rooms in the future. I am looking to floor a small part of roughly 17sqm to use mainly as storage.

Am I right in saying the proper method is to put down new joists (maybe 6 x 2) perpendicular to current ones.....roll out insulation and then OSB on top ( run this perpendicular to new joists)

The above space is directly over an unused bedroom so could I also just feck the insulation off to the side and just OSB onto current joists for the time being? Would save a lot of hassle. The house is A3.

Mellor

Additional joists required to maintain insulation thickness (and A3 rating). You’d need to verify that the existing joists can hold the extra weight.

Removing insulation is not a great approach. Will impact heat loss.

If converting to habitable rooms, you’ll need to fire rate the landing and hallway.

Sleeper12

Loft legs are your friend. They can be as tall as 300mm. This allows 400mm insulation in total under your new floor. Google loft legs

windowcills

You mentioned its above an unused bedroom

Cheaper and safer to put the insulation back as it was and just use the "unused bedroom"

AmpMan

https://www.boards.ie/discussion/comment/120848487#Comment_120848487

🙄 why do people feel the need to post crap like this?

wolfyboy555

https://www.boards.ie/discussion/comment/120845645#Comment_120845645

I assume existing joists are ok to hold any weight as the attic is designed to be converted in the future. I'm only using this area as storage for the moment. Xmas tree , suitcases etc . I'd only be removing top layer of insulation as there is some still between original joists. OR should I go to trouble of raising the entire area first with 6 X 2. I think the top layer of insulation is about 150mm.

https://www.boards.ie/discussion/comment/120848449#Comment_120848449

yeah I've looked into them but seem to be hit and miss reviews of them.

https://www.boards.ie/discussion/comment/120848487#Comment_120848487

when I say unused I mean there is a bed for the odd visitor who is over so wouldn't like the place full of junk.

standardg60

https://www.boards.ie/discussion/comment/120850328#Comment_120850328

I'd have also thought the existing joists would be deep enough to be floored straight over, are they 150 deep or 270?

The insulation you've removed can be put between the rafters instead, leave a gap for ventilation between it and the felt. Use a DPM to hold it in place if you're not going to sheet it now.

Sleeper12

Don't forget 300mm insulation is the minimum by today's building regulations. 400mm in an airtight home. It's well worth raising the floor to get 300mm

wolfyboy555

https://www.boards.ie/discussion/comment/120850554#Comment_120850554

the current joists seem to be 220 deep. There is a layer of 150mm insulation in between at the moment. Never thought about putting upper layer into rafters . Would that have much effect considering the rest of the attic (majority of it) won't have any in them?

https://www.boards.ie/discussion/comment/120850611#Comment_120850611

yes looks like it's 150mm inbetween joists and 150mm laid on top that I've rolled back.

was thinking these OSB :

https://brooksonline.ie/tongue-grooved-4-edge-18mm-osb-2440mm-x-590mm-norbord182

and these for joists ?

https://brooksonline.ie/44mmx150mm-2x6-whitewood-rough-fsc-2-swn044150

how far apart should I space the new joists ?

standardg60

https://www.boards.ie/discussion/comment/120851275#Comment_120851275

Sorry yes I meant 220. Those joists are designed to carry the floor so no need to increase them.

If you were converting fully you'd be insulating the rafters anyway so may as well do it now. Bearing in mind the osb will have an insulating value too I don't think you'll suffer much heat loss through the area you're flooring, you could top the existing 150 layer up to the 220 too before you floor.

standardg60

https://www.boards.ie/discussion/comment/120850611#Comment_120850611

Raising the floor could affect allowable height regs, it's designed to be directly floored over imo.

windowcills

https://www.boards.ie/discussion/comment/120849760#Comment_120849760

I laughed at the empty room and wanting more when reading it

Cousin got her attic converted and she carrys a hot water bottle in winter

Heat rises so the attic will now be the hottest room in the house, heat flow rate through material speed is porportional to temperature difference, so attic will want to have flawless insulation or the front porch and the landing will be showered with cold air (cold falls), most rooms are only 1 door from the front porch and landing so they will loose heat too

Sleeper12

https://www.boards.ie/discussion/comment/120851913#Comment_120851913

I know OP says attic is designed to be converted into a room but I doubt it is. There will be a steel structure up there if it is designed that way. Obviously if it is actually designed to be converted to a room then 300mm has to be part of that design. 300mm in the floor or pushing it to the rafters is still 300mm taken into account if designed to be converted. As I say if designed to be converted then OP will be able to see RSJs up there.

For the moment OP only wants storage. Last thing he needs to do is reduce insulation just for storage. This storage floor will be coming out if he ever converts into a room.

I don't understand being worried about the height regs & ignoring the minimum insulation regs

standardg60

https://www.boards.ie/discussion/comment/120852042#Comment_120852042

You're confusing a post construction conversion with one that's been designed in.

220mm trusses don't require steel, they'll carry the weight on their own. I have the same construction on my own house.

Sleeper12

https://www.boards.ie/discussion/comment/120852163#Comment_120852163

Regardless, if it was designed to be converted then a minimum of 300mm has been provided for insulation

standardg60

https://www.boards.ie/discussion/comment/120852554#Comment_120852554

The 300mm is irrelevant once it's been designed to be converted though, it's not the attic anymore. That is the difference, if the OP transfers half of the insulation to the rafters then there's still 300mm of insulation. Obviously I'm ignoring the bare block at the gable which would need to be insulated too.

In my experience the converted attic does indeed feel warmer in summer and colder in winter given it only has the 150mm in the rafters, but the rooms below the conversion retain the heat far more than those that aren't, even though they only have 150 above them. A combination of I assume flooring and the conversion being heated too.

Mellor

https://www.boards.ie/discussion/comment/120850554#Comment_120850554

You can’t just spilt the insulation half in floor and half in attic. And you do not want to use a DPM or you’ll trap moisture.

https://www.boards.ie/discussion/comment/120851975#Comment_120851975

Heat rises bit that doesn’t mean it all gathers in the attic. Hear also seeks equilibrium via conduction. The attic is highly unlikely to be the hottest of the heating system is downstairs.

The landing is also not going to be showered with cold air. Where do you think this cold air is coming from?

https://www.boards.ie/discussion/comment/120852684#Comment_120852684

The 300mm is not irrelevant once converted. The attic is irrelevant, the house still has a roof that needs certain minimum insulation for compliance.

If you spit the insulation to create a buffer zone. It can work, but it’s much more complicated than just “half it, be grand”. You’d need insulated doors, Aldine heating etc to make that work

Sleeper12

None of your plan meets the minimum building regulations.

150mm in the rafters & 150 in the converted floor only gives the house 150mm installation and not 300mm required in the regs. A builder can't sign off this on completing the work. If OP insulates the bedroom floor with 150mm it doesn't increase the house insulation to 450mm. The only insulation taken into consideration if insulation on the outside of the living area of the house. Outside walls,attic floor etc. If the attic is converted into a room then the insulation gets pushed to the rafters. I attic is designed to be converted into a living space then this would have been taken into account & here should be enough space for the insulation and 8 foot or so head height.

It's a pointless argument anyway. OP has an attic and plans to use it for storage. This is what he needs advice on. He may never convert it but if he does everything he puts in now, loft legs, floor and insulation will all be ripped out. They are two totally separate jobs. OP needs concentrate on flooring for storage & put converting out of his mind. There is nothing OP will do now that effects converting later

OP the insulation is vital in the attic. Don't reduce it in any way. Personally I'd go 900mm loft legs & use this height to increase the installation from 300mm to 400mm

d_dools

Instead of loft legs, I cut up some pallets and put them across the beams, then put the click-in flooring on top of that(in the opposite direction).

It raised the floor enough for the insulation.

Worked well for storage.

removed it all when i got it converted properly.

wolfyboy555

Thanks all for advice finished up today. Decided to raise it all up on 6 inch joists to accommodate insulation. Made a little step at start near hatch as it was akward stepping up from ladder due to layout. V.Happy with end result.