Raising joists in loft for boarding

[wg100]

I've recently moved into a 1950s era semi-detached house. The loft is quite large, but unsuitable for a loft conversion (roof pitch too low), therefore we're looking to:

a) add insulation as it's only got 100mm at the moment.
b) raise the level of the existing joists to allow the additional insulation to be installed and loft boards on top of that.

The existing joists are about 4.8-5m long, 4"x2" at 400mm centres. They rest on the external walls and are supported almost mid span by a perpendicular internal wall which goes to the base of the house. The area I'm looking to board over is about 25m2.

I'm looking to raise the floor level with 6"x2" timber to allow for the new insulation to go down without being compressed.

My questions are:

a) Can the new timber simply be laid on top of the existing joists (obviously screwed in)?
b) If not, should the timber be laid at right angles across the existing joists?

I've looked around and there seem to be conflicting views, so I thought I'd muddy the waters even further by seeking advice specific to my situation.

Thanks in advance. Will

 

[stef99]

You can raise the joist height with cheap light wood however, don;t put anything too heavy in there as the joist will not gain anystrength by adding wood on top.

If you say the roof is unsuitable for conversion, then I don;t see why you want to board the whole thing. Maybe a smaller area in the middle would be better?

You may not have mentioned why you want to board the whole lot, so I can assume theres some reason as to why you haven;t mentioned. But you will need to be careful of existing electrical cables also.

generally the jiost will take some stroage wight, but don;t push your luck unless you're going to replace or strengthen the existing joists.

Personally I would just add the wood along the joists. but don;t stick too many screws in as it will weaken the old joists.

far better to add some cross members in and only use a few screws into the old joists.

Letterally about 5-or 6, depeneding on the joist you already have.

 

[wg100]

My thinking was that by adding timber on top of the existing joists (so that insulation can be installed with out being compressed), then the load would be spread further. If I just constructed a raised platform in the centre of the loft, then the load would be concentrated on a smaller area?

I'm looking to board the area between the purlins which equates to around 20m2. We've got a lot of stuff to store whilst we do some renovation works to the ground floor of our house, then it'll be the usual Xmas decorations, luggage, odds and ends, etc. Plus by boarding a larger area now, it future proofs for any further storage needs.

 

[stef99]

well, if you want to baord it more, thats upto you...
I;m not going to argue with what your looking for...

However, have you thought about maybe sticking insulation in the roof and boarding that? I expect it may end up costing the same depending.

Either way, you can add wood on top crossways or lengthways.

Crossways would be technically better, but you will need to add 200mm in order to add the 200mm insulation which is part of the minimum regs.

(if you are working to the regs).

You will need to use noggins to keep it from collapsing onto the old joists.

You don't want that collapsing on your ceiling!

I personally would just make a frame out of wood, and screw a few chip boards down.