Boarding Loft - Insulation Advice & Pinning

[rossbardon]

Hi,

I wish to board my empty loft. In order to do this, from what I have read on here I should add 4x2 battens running perpendicular to the existing joists spaced 400mm apart. I should then have insulation in-between the existing joists, and a crossing layer in between the new battens. Then the floor boards should go on top. All sounds good.

Two questions:

1) Achieving the recommended insulation thickness of 270mm is going to be a problem. The current joints are 100mm deep. If I put the 4x2 battens on top that will give me another 100mm of insulation. So total will only have 200mm. Any advice? It seems impractical to use bigger battens then 4 by 2?

2) How should I fit the battens to the existing joists? Simply screw the battens into the existing joists just to simply position them? Is this added weight (of the battens) + the floor + storage acceptable for the loft joists? (the house is a 1930's semi)

Thanks in advance, great forum!

 

[freddiemercurystwin]

200mm of insulation will be fine, the following thread is slightly confusing but follow the posts I made and you'll not go far wrong: //www.diynot.com/forums/viewtopic.php?t=284959&start=0

 

[rossbardon]

That link is incredibly helpful link. A near identical problem to my own solved there. Excellent, thanks.

I'm still a bit uncomfortable with only having the 200mm of insulation but I cannot see what else I can do in this instance without raising the floor excessively high (all of which is eating into the available storage space).

Two final questions regarding the insulation:

1) The loft was insulated by the previous owner with a government grant; unfortunately for me in this case there is an excessive (300-400mm) depth of insulation. The first maybe 50-75mm of this insulation is old brown / wool insulation (I guess they just threw the new stuff on top of the old stuff). Should I go to the trouble of ripping this old stuff out and using only the 'newer' insulation. Does the fact I will only have 200mm of insulation space have any weight to the argument?

2) Do I need to leave an air gap between the insulation and the board, if so how much?

Thanks.

 

[freddiemercurystwin]

Do not bother removing the old insulation it will just make a hellova mess getting it out the house and is still working OK anyway. You can squash the new insulation down a bit it won't do any harm, frankly you could use 150X38 timbers to raise the floor more if you wish to have a bit more.

You should not have an air gap.

 

[rossbardon]

No air gap? Ok I thought that was needed for airflow?


Final question (I promise), What should I do about the perimeter were the eaves are? Leave a gap? or can I board out until I butt up against something

 

[freddiemercurystwin]

An air gap is required if you were insulating between the rafters rather than at floor level. For a floor an air gap is not required. You need check that any insulation you bed down in the eaves does not block the flow of air flow from the eaves vents (be they soffit vents or gaps under the tiles or whatever) and the space inside the loft. There is little point boarding right up the eaves anyway as it will just be difficult to get access and be of limited use anyway. You should not be putting so much up there that you need every available square inch.

 

[rossbardon]

Ok thanks.

For the raised cross sectional joists. Do you think it would be ok to use basic low cost timber studding?

Whislt the timber studdings do nnt have a square edge and are not treated, I cannot see why I would need expensive C16 square edge timbers? Or am I missing something?

 

[freddiemercurystwin]

Aye they're only cosmetic so need for treated or structural timber what do you mean your choice of timber is not square edged though?

 

[rossbardon]

I was going to use these cls studding timbers:

http://www.diy.com/nav/build/timber...ber-L-2400-x-W-63-x-T-38mm-9275994?icamp=recs

THey have radi on the edges. Not square.

 

[freddiemercurystwin]

Ahh OK you mean the corners not the edges lol! I guess corners would be better than none but really when the decks on and its all screwed up tight it isn't gonna move, you could add a row of noggins if you're that worried. B&Q are a bit of a rip off on some things btw so try the merchants for your timber!

 

[rossbardon]

Hi, well this weekend the project starts. I've decided to gut the loft of its existing insulation and put down some new stuff.

So the first layer of insulation going in between the existing joists. I've brought some 'Knauf Eko Base-Layer 100mm thick' (this stuff is ok?). This amount of insulation will bring me flush with the existing joists.

Then I am fitting perpendicular joists (using 4 x 2 timbers), giving me room for only another 100mm layer insulation. I am just going to live with being 70mm short on the insulation, I cannot see what else I can do?

But the question is, what about this second layer layer? Usually you would put down 170mm 'top up layer', but with only 100mm space do I just put down another layer of 100mm BASE layer? Is there actually any technical differences apart from the thickness's between these 'base' and 'top up layer'? It is just not clear on the packages.

 

[mointainwalker]

Hi, well this weekend the project starts. I've decided to gut the loft of its existing insulation and put down some new stuff.

Very foolish. You are

1) Creating lots of extra work and dirt in your house
2) Creating lots of waste you have to dispose of and then someone else has to dispose of ( increased costs to your local council coming back to you later).
3) Spending extra money unnecessarily.

and all this ...


To achieve no increase in energy efficiency if you replace it with the same thickness.

Base and top up is the same insulating-material although the top-up may not have a vapour-barrier backing( brown paper ) because it is assumed that it will already be on the base layer already in place.

Think again before you start this exercise in futility.

 

[xr4x4]

If you had two layers of 100mm standard fibre loft installation, so a total thickness of 200mm.

If you squished this down to 100mm, would it only perform as 100mm?


Ie if you squished down a total of 200mm insulation inbtween the joists, (so now a total thickness of 100mm) and boarded over the top, would you reduce the performance of the insulation?

 

[rossbardon]

Hi mountain walker.

I appreciate your opinion is fair on not gutting the insulation, but the practicality of working within the existing insulation, rubbish and mess up ment it would be impossible to work within.


I've now gutted it.


So this brown paper vapour barrier. Your right its not on the insulation. I can buy a barrier and apply it separately? AT what layer. Before the base or after the two layers of insulation?

 

[mointainwalker]

I can buy a barrier and apply it separately

Sure. Just buy a thin poly sheet of the type used by decorators for protecting against paint spalshes and drape it over the ceiling and joists before putting down the insulation.

Remember not to insulate under any water-tanks you may have up there and keep power-cables ( not necessary with lighting-circuits ) above the insulation to prevent possible over-heating.

Edit: Have just re-read your question. You only need one vapour-barrier irrespective of how many layers you put down, so if one of your purchases has it, then you don't need a second, but in this case the rolls have to be laid paper-side to ceiling.