Cross battening loft + insulation advice

samuki

Hello All. Can anyone please advise. I'm hoping to board the loft to use for light storage. When I went up I noticed the state of our insulation. It's really tatty and torn wool type insulation, and is only 10cm deep in some places. In other areas, it's non-existent. I obviously need to increase level of insulation to the recommended 27cm. The joists are 2 x 4 so can only put an initial layer of 10cm (I'll remove all old insulation).
I considered laying the Knauf Supadeck :eek: but I'm not a footballer!!!

As such, is it safe for me to cross batten with 2 x 7 or 2 x 8 beams (from B&Q) thus giving me the additional 17.5cm space to increase insulation and also lay down loft boards? Alternatively, should I cut out 2 x 4" blocks and attach these to the joists, THEN lay 2 x 4 beams on these blocks? If either one of these methods is OK, what's the best way to attach the beams to the joists? Can you get 9" or 10" screws? Should I use 90 degree angle brackets? Also what's the best way to safeguard the electrical wiring?

In addition, we've recently had GCH + combi installed and the pipes had to go through the loft space (the pipes are well insulated), Is it safe to insulate around these too? I'm considering boxing these using plywood as there are pipe joins and valves, to allow access should anything go wrong. Any advice? Can I also remove the cold water tank and the raised base it was on? All pipes to the tank have been disconnected and it's completely drained.

I'm a capable DIY'er so long as instructions are easy to follow. Pictures help too!! Any advice is welcome and greatly appreciated.

WaveyDave_2

In my house, we have one layer of insulation running between the joists, then there is another layer running across the joists. To board my loft, I bought 2x4 and cross battened between the runs of insulation (running across the joists). I found that the width of the boards I used was pretty much bang on to the width of the run of insulation, if you see what I mean?

savemoney

That Knauf Supadeck is very expensive btw

If you lay new rock wool insulation then in must not be flattened by loft boards. Also when loft insulation is laid down now by contractors they tend to lay it both across and along the joists so no good for laying loft boards

The EST recommend increasing the height of the joist to lay rock wool across the joists and then boarding above

27col

The first thing that I would say is, to only board the minimum area that you need for storage. If you need a huge area, then might I suggest that you are just hoarding things for the sake of it. If you use 2x7 or 2x8 beams they will cost you a lot of money to install and add considerably to the weight that the existing ceiling joists have to carry, long before you add the weight of the flooring material and the weight of the stored goods.
What ever means you decide to use, you do not need 8" screws, you just need to spike the new joist to the existing joist diagonally towards the bottom. You can do this with a 4" nail or screw.
A good compromise would be to just board the minimum area around the hatch that you think that you need, after due consideration of what you want to store. Then just roll out some of the wide 150mm thick insulation everywhere else. Do not bother to remove the old insulation, just cover it up. It will be an obnoxious job. I know from bitter experience. I pulled down an old bungalow to build my house and reused the old insulation under the new. This was in the days long before insulation was jacketed in polythene, it was a disgusting experience.
Ideally the wiring should not be covered by insulation, but upstairs lighting circuits are normally very lightly loaded so should not overheat. If there is enough slack in the wiring, then pull the wires clear of the insulation if you can, but don't worry if you can't.

samuki

Thanks for all your responses.
After ALOT of research, I think I've come across a suitable alternative, Warmcel 100. To achieve a U-value of 0.17, I'd only need 200mm of the stuff compared with 255mm of regular glass wool. This means I can use 2x4 beams to cross batten. Cost-wise I'm looking at spending approx £4 per sq metre. It's still dearer than £2 per sq metre for glass wool (not accounting BOGOF offer) but considering my limitations seems the better option.
In case anyone else was wondering, Pavatherm insulation board works out at approx £11 per sq metre and Celotex GA3000 insulation board is £12 per sq metre.

bobdauilda

What is the thinnest board insulation that will give the equivalent u rating for rock wool insulation of 270mm? Is there any government grant available for insulation other than rockwool?

ic

Unless you want one hell of a filthy house, don't remove the old insulation - just put new over the top (in the areas you're not boarding).