Any builders out there?!!!

[Black Bug]

Looking for a bit of advice/ideas before approaching local builders - a vague attempt to prevent getting ripped off 'cos I'm a bit clueless about building stuff.

Here's the problem, my house is a 1903 detached place on the edge of the fens, brrrrr, it's fecking chilly! Loft insulation is seriously lacking, there's a 3-4" layer of rockwool type stuff in there at the moment, so I want to up it to the current suggested depth of 10.5" (how random?!!) hopefully by a grant thing from local council (however that works). Problem is that the joists are only 4" deep as that's all they bothered with back in those days. The problem is compounded by the fact my gf wants to use the loft for storing her VAST amounts of junk, so it needs to be boarded up to support that junk. When we bought the place the surveyor said not to put any load on the 4" joists (which seems reasonable to me). Also there's no point in putting in 10.5" of insulation just to squash it all down under boards. So what I need is new joists in there to a) give me a 10.5" gap for the insulation and b) be strong enough to allow boards to be laid and VAST amounts of junk to be hidden up there.

The loft is about 30' square with joists running front to back it seems. So how the hell do you go about putting in additional joists to span that gap safely? Typically the loft hatch is in a side room (and tiny at the moment) so it's not really practical to drag large timbers upstairs, round a corner and up the hatch. Would the builder just make a hole in the roof and put get them in that way? I guess there has to be another joist that goes across the width of the house centrally that the front/back joists attach to, they can't be 30' long surely? Would the new joists have to be 2x10ish and bolted to the sides of the existing joists, or could 2x6ish timbers be used that sit on top of the existing timber, cunningly attached some how? From what I can see the joists are not much more than 1' apart, so would everyone need to be built up, or say just every other one? Sorry I can't give better info on how the joists are laid out, but I can't actually get in the loft as I haven't got a long enough ladder, and it's all covered up in there with sheets of plywood, so you can't see the joists anyway.

Any info is much appreciated! Any rough ideas on costs would also be interesting to hear!

Cheers,
Rob

 

[speedemon]

I am not a builder, but I know a lot of builders and I have worked for a lot of building companies, and I would say that sounds like a roof off job then new joists put in. As for cost you are looking at over 5k.

 

[Black Bug]

Def not in the mood to loose £5k, odd that isn't it

Not that I desperately want to DIY it, but I guess I could man-handle 10' joists up in to the loft myself. Any thoughts on if these would be strong enough if they were attached end to end with nail plates then place next to an exising joist and bolted to that joist?

S'pose I should get up in there somehow and lift the plywood sheets so I can at least see how the joists are laid out.

Cheers,
Rob

 

[Arkwright]

Don't go there. your 4.5" of wool will be laid between the joists. The extra wool should be laid accross the joists at rightangles to give improved insulation. Adding extra thickness of joist will be very expensive plus boarding out on top of that . Tell her to dump the crap it'll be a lot cheaper.
I think Steve Burns could perhaps advise you better.

 

[STEVE BURNS]

without seeing the actual roof and existing ceiling joists it is a bit difficult but the ceiling joist should run the same way as the roof rafters and they should be sitting on a wall plate at the outside wall and probably be sitting on a center wall to ease the lenth of the span

you should be able to sit your new joists on the outside plate with the ends cut at a splay so they do not obstruct the line of the tiles

If you want to discuss further give me a ring

 

[zeeman1972]

Having done a few of these jobs in a past life, it would be worthy to note that you will most likely have to re-run a fair quantity of the lighting cables in the loft space if you do put new joists in. The cables are most likely going to be running close to or totally in the way of your new timbers.



I have done a similar job in my own house and without labour I reckon, for the size of loft you describe, you are looking at about £800 for a fully boarded reinforced set up.

 

[Black Bug]

Ta guys,

Attached is a little pic (cos I like drawing) of roughly how the top floor looks if that helps. I presume that the wall with the chimney in is load bearing, as is the wall with the staircase on.

If all the joists do run front to back, then there must be some sort of backbone that runs side to side (on top of the chimney wall) otherwise the joists over the landing must be well overspanned

Good point about the lighting cables, they must be lurking up there as well. As is the odd collection of tanks that pretends to be an excuse for plumbing. Good opportunity to shift those to a corner and make them a bit more solid.

£8-1000 is a more bearable cost, has to be said. Need a holiday up north Zeeman?!!

Cheers,
Rob

 

[260ZG]

Current insulation standards under part L1 of the Building regulations would require 100mm Glass fibre quilt between joists and 150mm laid at 90 degrees over joists. However..... you don't have to use Mineral wool or Glass fibre. If you used a UF foam based board, such as Celotex you get the same insulation but with a thickness of 100mm, although it is more expensive.

As to strengthening the joists, it is a bit difficult without seeing it, but for a loft conversion it would be normal to bolt or nail 200 x 50 joists to the side of the existing keeping them up from the top of the ceiling surface 25mm.

Normal max span for a 100 x 50 C16 grade, used as a floor joist at 400 centres is 1.93m

Hope this helps

 

[Black Bug]

Thanks Colin, that's useful info for sure. Had a good chat with SteveB last night which definitely helped get my head straight on a few things too, thanks Steve. I'll have to get my bum up in the loft this weekend and get a better feel for how things really work up there, then I can start figuring out the finer details.

Cheers,
Rob