Loft insulation and chipboard flooring (with pics)

[GaryMo]

I've just installed 100mm loft insulation between my existing 3x2 roof joists with the next step being to run a number of new 3x2 timbers across the existing roof joists therefore creating an area to fill with 170mm insulation. I'll probably fit the new timbers with the 3" side up to give more height.
On top of this I would then like to lay a chipboard floor.

A couple of questions........

This seems daft and I *may* regret asking but will anyway......If I was to compact 170mm roof insulation into a 75mm area (ie between existing joists and new chipboard floor) will any of its insulating properties be lost?

Lastly, will general chipboard flooring be adequate for a loft or should I use the green treated chipboard?

[GaryMo]

A slight rethink......

I have two purlings(?) running the full length of the loft, one on either side.
I'm now thinking about running 4x2 between them and fixing to the purlings with joist hangers then putting chipboard on top.
That way I'll have more than enough space to install 170mm insulation and I should also get a stronger flooring which won't put unneeded stress on the existing joists and ceiling below.

[GaryMo]

Bump for a couple of answers please

A couple of questions........

This seems daft and I *may* regret asking but will anyway......If I was to compact 170mm roof insulation into a 75mm area (ie between existing joists and new chipboard floor) will any of its insulating properties be lost?

Lastly, will general chipboard flooring be adequate for a loft or should I use the green treated chipboard?

[Deluks]

GaryMo wrote:

A slight rethink...... I have two purlings(?) running the full length of the loft, one on either side. I'm now thinking about running 4x2 between them and fixing to the purlings with joist hangers then putting chipboard on top. That way I'll have more than enough space to install 170mm insulation and I should also get a stronger flooring which won't put unneeded stress on the existing joists and ceiling below.

erm, I think those purlins (no G), are holding up the joists and ceiling below. What are those cut ends in the picture, what were they before, do you have any before pics??

[GaryMo]

The cut timber lead all the way to the peak like the blockwork which is on show.
I've just had a two storey extension built on the side of my house. The existing roof was dormer with flat roofs to both front and back. The main roof has been converted to a conventional roof to match in with the new extension.
The flat roofs are still on show on the outer sides of the purlins.
The purlins are supported by resting on the blockwork either side.

If I was to go for the easy option and counter batten the existing ceiling how would I maintain the required thickness of insulation?
I've already squashed 100mm in between the existing 3x2 joists so would need a further 170mm but this would need a lot of compressing if I was to use 3x2 battens. If I used larger battens then this would put more stress on the ceiling.

What would you recommend?

[salem2000]

Am I missing something, what is stopping the roof structure from spreading outwards. Did you remove any timberwork yourself or was this done by your builder.

What do you intend to use the loft space for?

[GaryMo]

All done by a builder to relevant building standards, it's been specified, built and passed.

Loft space will be used for general light storage - suitcases, christmas tree / decorations etc.

[salem2000]

Deluks wrote:

erm, I think those purlins (no G), are holding up the joists and ceiling below. What are those cut ends in the picture, what were they before, do you have any before pics??

In picture three it does look like the ceiling joists are supported by the purlins. I would be inclined to use joist hangers on the perlins to support a secondry floor level if adding more timber.

Salem.

[GaryMo]

salem2000 wrote:

In picture three it does look like the ceiling joists are supported by the purlins. I would be inclined to use joist hangers on the perlins to support a secondry floor level if adding more timber. Salem.

That's my thinking. The span between the two purlins is 3 meters, would a 4x2 secondary floor level be OK or would I need to go for larger timber?

What if I was to use 4x2 and make it so the bottom of the 4x2 runs across the 3x2 which runs end to end in the centre of the existing joists. That way there'll be joist hangers either side and the 4x2 would have a little support in the centre.

[masona]

Can you take a photo of your roof spec, I'm a bit concern the new rafters with no purlins

[GaryMo]

Existing roof which used to comprise of 2 dormer flat roofs, now changed to standard pitched and tiled:





New extension roof:



Spec for new and redo of existing roof:

[masona]

Okay, I see how it done now!

It's a shame to use it for loft storage, make it into a study room with velux windows will need at least 7"x2" joist between the 2 ex-purlins