DIY Doctor

Loft Insulation under Loft Boards

Postby D@ve » Sun Nov 08, 2020 3:03 pm

Hi all.

Newbie. First time post.

I am in the process of boarding out my loft for storage. Before I do so I would like to insulate it first.

Ideally I would like to keep the job as simple as possible therefore I am considering just insulating between the original joists and then boarding straight on top.

The original joists are only approx 75mm tall so that would mean 70mm insulation between the joists without the boards compressing it.

I am aware of the 270mm building regulations but that would mean I would have to raise the floor to accommodate this thickness. Don't really want to do this. Plus the 270mm doesn't factor in boards on top do they? So the boards I lay on top will help to insulate too wouldn't they?

I have just read an article which discusses the diminishing returns of loft insulation and anything past 100mm is relatively(ish) not that effective(ish).

So I am thinking to make life easier for me I think I could get away with what I have suggested.

My questions to the forum is:

1. What type of insulation will give me the best insulation at this thickness.

2. Is this a good/bad idea?

3. Anybody got any other solutions/advice.

Looking forward to your replies.

Thanks

D@ve
D@ve
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Postby stoneyboy » Mon Nov 09, 2020 10:43 pm

Hi d@ve
Once you have boarded on top of the 75mm joists it will only be good for lightweight storage. Consider fitting 100mm joists on top of the existing in areas where heavier items will be stored. You can then have 175mm of insulation.
Regards S
stoneyboy
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Postby D@ve » Tue Nov 10, 2020 3:25 am

Hi stoneyboy. Thanks for the reply.

Considering your suggestion, I have a couple of thoughts.

I am not sure if you mean laying 100mm battens directly onto the current joists. Granted this would give the extra height but would also create more weight on top of the joists before I even start storing things anyway.

If you mean properly installing new joists independent of the existing joists. This would be to big a job than I want this to be.

Thanks for your reply though.
D@ve
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Postby stoneyboy » Tue Nov 10, 2020 10:30 pm

Hi d@ve
Your existing joists will be resting on walls below and will have bowed downwards over the span between walls. You should be able to instal extra joists so they are supported on or close to where the joists below are supported.
Regards S
stoneyboy
Rank: Project Manager
Posts: 3857
Joined: Wed Dec 10, 2008 6:44 pm



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