Attic Flooring

BGozIE

Hi all,

Sorry this post has been done a few times - finding conflicting info.

Recently moved into a new build. I want to floor the attic.

The current insulation between the ceiling joists is 300mm Rockwool (as far as I can see).

Query I have is, is it ok to put osb directly onto the ceiling joists and therefore directly on the insulation?

Another question - The space I want to floor is about 400square feet. I had considered doing it myself but decided against that. A local builder has quoted 1100 to do this. That seems good, but I'll get more quotes tomorrow. Is it too good?

I appreciate the advice/input.

dathi

BGozIE wrote: »

Hi all,

Sorry this post has been done a few times - finding conflicting info.

Recently moved into a new build. I want to floor the attic.

The current insulation between the ceiling joists is 300mm Rockwool (as far as I can see).

Query I have is, is it ok to put osb directly onto the ceiling joists and therefore directly on the insulation?
.

https://www.ie.screwfix.com/birmingham-innovations-loft-storage-stilts-150-x-210mm-pack-of-12.html?utm_source=Google&utm_medium=CPC&utm_campaign=Shopping&gclid=EAIaIQobChMI4u_p6M3f3AIVLbvtCh2RMAcXEAQYASABEgLdGvD_BwE&gclsrc=aw.ds

use loft legs to stop the boards from compressing the insulation

BGozIE

Great, thank you!

Calahonda52

What depth are the ceiling joists?

BGozIE

Calahonda52 wrote: »

What depth are the ceiling joists?

They look to be about 8" - I'll measure tonight. Would that be right for a ceiling joist?

BrokenArrows

BGozIE wrote: »

They look to be about 8" - I'll measure tonight. Would that be right for a ceiling joist?

You shouldn't compress the insulation, it loses its insulation ability when compressed.

If the insulation is less than the height of the beams then yes you can just put some boards on top.

BGozIE

BrokenArrows wrote: »

You shouldn't compress the insulation, it loses its insulation ability when compressed.

If the insulation is less than the height of the beams then yes you can just put some boards on top.

Thanks for that...the insulation is certainly higher than the joists, also in some cases is just thrown over the joists.

It was a show house so maybe they wanted it to be really warm, so they could talk about how well insulated the house is. The insulation in the attic is certainly haphazard.

Lumen

BGozIE wrote: »

Thanks for that...the insulation is certainly higher than the joists, also in some cases is just thrown over the joists.

The normal method is to have one layer of insulation between the joists, and another across the joists at right angles. This stops the cold-bridging effect of heat escaping through the joists.

For this to work properly the first layer must be exactly the same depth as the joists.

Which isn't difficult, since both joists and insulation are manufactured in a small number of standard sizes.

This is simple stuff. Getting it wrong is just sloppy.

dodzy

Lumen wrote: »

The normal method is to have one layer of insulation between the joists, and another across the joists at right angles. This stops the cold-bridging effect of heat escaping through the joists.

For this to work properly the first layer must be exactly the same depth as the joists.

Which isn't difficult, since both joists and insulation are manufactured in a small number of standard sizes.

This is simple stuff. Getting it wrong is just sloppy.

I’ve never seen ceiling joists the same depth as insulation. No builder is going to put 10” joists in the attic.

Lumen

dodzy wrote: »

I’ve never seen ceiling joists the same depth as insulation. No builder is going to put 10” joists in the attic.

I don't mean that total joist depth is the same as total insulation depth, I just mean that the first layer of insulation (between the joists) is the same depth as the joist.

I'm fairly sure I have 4" joists in my attic (mid 1980s build), and I did have 4" insulation until I pulled it out.

HoboJoe

Flooring can weight a lot when added up. This is compounded by the fact that you might use the space to store or hold more weight. Many of these joists are not designed to store much if any weight at all.

Sure an engineer will just tell you to include steel beams between between gable walls but it might be worth the 200 euro to call one out if it's potentially dangerous.

Calahonda52

Lads, no need for a dog fight: we all want it done right so lets try an agreed communique
:
Perhaps
The normal method is to have one or more layers, of insulation between the joists, and another across the joists at right angles. This across layer stops the cold-bridging effect of heat escaping through the joists, which can be 10%.

For this to work properly the one more layers between the joists must be exactly the same depth as the joists.

Edit to suit

BGozIE

Thanks for all the input. So if I floor it I loose the right angle overlapping insulation anyway?

I've decided I'll only do some of the attic for storage so as not to lose too much insulation.

Thanks again!

dathi

BGozIE wrote: »

Thanks for all the input. So if I floor it I loose the right angle overlapping insulation anyway?

I've decided I'll only do some of the attic for storage so as not to lose too much insulation.

Thanks again!

not if you use the loft legs
https://www.youtube.com/watch?v=hrnIndaiPB8

ErinGoBrath

Apologies for hijacking but I'm also looking for advice.

We're in a new build. Web trusses are 22inchs apart. 1.5in x 3.75in

Seems quite lightweight?

Would they take some loft legs and osb board for general storage?

dodzy

ErinGoBrath wrote: »

Apologies for hijacking but I'm also looking for advice.

We're in a new build. Web trusses are 22inchs apart. 1.5in x 3.75in

Seems quite lightweight?

Would they take some loft legs and osb board for general storage?

you'll be fine, dont forget you've all the room & landing partition walls that add hugely to the strength of the joists that you'll be flooring.