Raising loft floor above 200mm Rockwool

[JayW]

Hi Guys

Firstly im not a builder so I apologise if I don't explain it clearly.

We have recently bought a 1930s house and we wish to board out the loft for storage.

At the moment there is some very old rockwool (must be 70-100mm) between the joists, the joists are 70mm deep.

On top of this is 200mm worth of new rockwool insulation laid perpendicular that the previous owner had as part of a scheme I believe.

We wish to board over this but how do I raise the joists by 200mm?

The typical approach I see is 4x2's cross battened however this is too shallow for the 200mm rockwool, even 8x2 the insulation would need compressing slightly.

What is the best thing to do? I have looked at the loft stilts and was thinking of getting rid of some insulation down the centre of the loft and putting 2 strips of 4x2 and plywood to make a walkway, then loft stilts at either side.

Or would 8x2's be okay? Would these not weigh quite a lot?

Any tips would be appreciated!

Cheers

James

 

[PrenticeBoyofDerry]

Firstly, I assume the reason for boarding is for storage?
You need to access whether your existing joist are structurally capable of carrying the load demand.

Existing 70mm joist, will need to support the additional weight of the
*Cross timbers
*Insulation
*loft panels
*Stored items
*Then the odd person being up there

 

[JayW]

Yes it will be light storage (suitcases, boxes, junk)

How do I best assess if the existing joists are capable?

I will try and get some photos tonight of where the joists are in relation to internal walls etc, they run width ways from the eaves.

Thanks

 

[JayW]

Hi guys

Got some photos and an update.

Would appreciate a quick reply as I can get the materials and start work this weekend

This is what im working with -

The solution I have come up with is to remove the old insulation and raise the joists with 2x4 and then put the 200mm insulation back down.

I will then cross batton with more 2x4 and put 100mm insulation perpendicular.

Please note the wood is just scrap for image purposes!

As you can see I have a brick wall and what I think is called 'binders' at the side, there is also another brick wall next to chimney.

What I need to know is if I go about is this way will the binder and wall do a good job of supporting this new deck?

It will be topped with either 18mm ply or chipboard, I was thinking ply as its lighter.

I would secure 2x4s with brackets and screws unless you guys think it is better to drill through the 2x4 downwards and into joist with long screws?

Also one of the joists is leaning slightly due to old age, how would I go about making it level when attaching 2x4?

Any tips welcome and like I say may start work today!

 

[pgriff35]

Sounds like a lot of work for extra insulation but if you're staying there for 10 years or so it's worth doing. I would just replace the old insulation and board over the existing joists.

 

[JayW]

If I did that and only had 200mm of insulation I would still need to raise the joists with the 2x4 like in the picture.

Would doing it like that be okay weight wise? How is best to secure them to the joists? Screw through or vertical brackets along the side?

 

[JayW]

Also ply vs chipboard? only used for light storage and walking on.

 

[james0james]

If that was my project all I would do is to replace the existing tired loft insulation with new that will fit in between the existing rafters,level them uprights to rafter level,level blocks to just below rafter level (angle grinder) then lay t&g 18mm chipboard (get long narrow lengths not standard loft packs) screwed down,never nail !.
Just do the area from your ladder to the far wall.
As per reduction in insulation performance,well who knows but its going to be miniscule.

Remember its for light storage only,i bet you wont !.

If you are wanting to spend more money use insulated loft flooring boards from http://www.encon.co.uk/products/view/965/ecotherm-eco-loft-25
there are also similar products and suppliers.

Edit search for ecotherm eco loft 25b.

Adding extra timber to raise existing rafter level,is possible but needs to be done by a competent person in relation to strength,fixings,electricial wiring,pipes etc.

James.

 

[JayW]

I do feel competent enough to raise the joists, it also seems the best option as sub 100mm insulation is just not enough!

The new timber will be secured to binder with 90degree fixing brackets then vertical brackets to the joists underneath, then I will put struts in between each section to give extra rigidity.

Thanks for the suggestion though!