Loft Boarding!!!

[bcfcjwb1]

Hi,

I’ve read through so many posts on this subject, but I can’t seem to find the answers I need – sorry!

Here are the basic facts…

My loft joists are ~70mm deep, ~32mm wide.

My current loft insulation is approx 100mm deep.

My house was built in 1998 and has a trussed roof.

I want to increase my insulation to the recommended 270mm and board the loft for light storage at the same time.

I know I need to cross batten in order to do this but have a couple of questions/concerns…

If I simply put the cross battens on top of the joists, the insulation will be compacted to 70mm, do I need to increase the height of the joists by 30mm? If I do, is it better to use one long piece of wood or small blocks at the appropriate intervals?

Assuming the 100mm existing insulation is fully usable, I could then top up the additional 270mm using appropriate carcassing timber. I am concerned about the additional weight of the additional cross battening timber and chipboard, should I be?

Access to the loft would be infrequent (6 times a year at most).

Thanks in advance

 

[PrenticeBoyofDerry]

There are a number of ways to do this, you could just go straight across existing joist and flatten the insulation in that area, it will compact easy enough and should not but too much downward pressure on the ceiling below.
You could also put the strips or packing blocks as you have mentioned.
The other alternative would be to remove existing insulation, replace with 70mm, then lay your existing insulation back down when you have raised the loft floor level and the build up the depth of insulation to the required amount.
As far as the extra weight is concerned, what supporting walls or structures do you have below and what distances are the spans between the supports?
It's unusual, to totally board a loft floor out, so be aware of that and don't be doing unnecessary work, also loft spaces are designed for light storage, so again be aware of that too!

 

[JohnD]

you might also consider laying flat expanded foam insulation slabs, with the ply or chipboard flooring on top of that. Then you won't need battens

You will find a display of this (quite new) method in your local DIY shed sponsored by a maker of expensive foam slabs in small boards, but I can't see why it shouldn't work just as well with the much cheaper large polystyrene slabs you can get.

Expanded polystyrene must not be laid where it is in contact with PVC sheathed or insulated cables, though, as the plasticiser leaks out

 

[PrenticeBoyofDerry]

Expanded polystyrene must not be laid where it is in contact with PVC sheathed or insulated cables, though, as the plasticiser leaks out

That's a good point:
If you do decide to use polystyrene sheeting as an insulator, PVC cables can have a chemical reaction with polystyrene, when in contact with it.
Running the cable through suitable conduit, leaving a non contact gap or using a polyethylene or polypropylene tape between the cable and the insulation, would resolve this.
Also if you have any cables running power circuits, such as showers and sockets, they do not want to be run through the insulation as heat can not dissipated, this will effect the current carrying capacity of the cable. Lighting circuits on fuses rated at 5A or breakers rated at 6A, protecting 1.00mm T&E cable will be okay, as the maximum de-rating of the cable will still allow 5 and 6 Amps to flow safely.

 

[bcfcjwb1]

Thanks for the replies so far.

I think I've decided against polystyrene boards due to cost - unless someone can point me in the direction of a reasonable priced product?

Some more information...

The gaps between the joists are 600mm, the loft span is 6 metres wall to wall - from one side of the house to the other. There are 11 supports wall to wall, they are shaped like a W.

The house is a 4 bedroom detached built in 1998. I was planning to board 20 square metres, not that it will all be used, just that I want it to be as easy as possible to use properly. All storage will be light and well spread.

To my knowledge the roof structure just sits on top of the brickwork at the front and back of the house. The walls upstairs are all studwork only.

My latest idea is to remove the existing 100mm insulation and use 100mm packing blocks to build up the existing joists to 170mm. Then add new 170mm insulation to this and cross batten using new 100mm joists, finally reusing the existing 100mm insulation to create the recommended 270mm in total.

How does that sound? I think my main concern is whether I will overload the loft trusses. If I want to be sure, who could I contact to give me a professional opinon?

Is it worth me uploading a picture?

Thanks again.

 

[PrenticeBoyofDerry]

My only concern would be the the stud walls, they could be structural stud but may not be. 6 metres without any structural support could be pushing it.
Your best advised by a SE(structural engineer) but they don't come cheap.
Do some calling around and explain what you need calculating.

 

[bcfcjwb1]

I'm going to upload a few pictures later when I can locate my camera!!

Thanks again.

 

[PrenticeBoyofDerry]

I'm going to upload a few pictures later when I can locate my camera!!

Thanks again.

I look forward to viewing them