Boarding Loft.
Discussion
We want to board the loft and at the same time increase the amount of insulation up there.
Roof trusses run front to back at 600mm to centres, I am planning to add an additional layer of floor joists running at 90 degrees to the roof trusses and with 400mm to centres, which will allow me a lay an extra 150mm depth, 370mm wide, insulation over laying the old stuff also at 90 degrees.
Then I plan to lay 2400 x 600 x 18mm floor boards on top of the new joists.
Any issues with this or is it the perfect plan?
Thanks
V.
Roof trusses run front to back at 600mm to centres, I am planning to add an additional layer of floor joists running at 90 degrees to the roof trusses and with 400mm to centres, which will allow me a lay an extra 150mm depth, 370mm wide, insulation over laying the old stuff also at 90 degrees.
Then I plan to lay 2400 x 600 x 18mm floor boards on top of the new joists.
Any issues with this or is it the perfect plan?
Thanks
V.
V12Les said:
Instead of another row of joists to gain height why not use Kingspan or similar inbetween the existing celing joists?.
Got to be careful of ventilation though, there's a risk of damp forming.OP-That's exactly what I did (though I used smaller boards), though your 400mm centres seem a bit excessive - 600mm would be better I think. With too many joists you have less space for insulation (is the u value higher for wood than insulation?), and you are adding A LOT of extra weight to the existing joists. Better to use lsighting thicker boards if needed (though I wouldn't worry in a loft. Be careful to get your cross joints totally flat and level (set a couple of datums), and measure your spacings from the first batten (not the last one you did) so any errors don't add up (compound tolerancing). My exisiting joist were all over the place, so I had a nightmare routing notches into the cross battens to get the tops of them flush so I could board. If the existing battens aren't flush you run the risk of stressing the ceiling underneath when you screw the boards down...
VxDuncan said:
Got to be careful of ventilation though, there's a risk of damp forming.
Very definitely. I could dell you some real horror stories about damp problems cause where there isn't adequate cross-ventilation of ceiling level insulation in trussed rafter roofs.There's also a potential issue with loading, if it's a 'modern' trussed rafter roof (mid '60's onwards, typically with a 'W' arrangement of bracing struts between the rafter and ceiling member on each truss). I won't bore you with the technical details, but basically these roofs are not designed to take the heavy loads from storage on the ceiling. They are carefully designed to take the loads from the water tank, and that's about it.
You may get away with it, but don't say I didn't warn you if you don't. If you store a large amount of heavy stuff up there (eg. paperwork or stacks of books or magazines), expect some distortion of the roof structure in the longer term.
Try useing kingspan between the floor joists (better, although more expensive, than ordinary loft insulation) then put down insulative floor boards (i think these also may be by kingspan).
As other have said, be wary of insulating roof joists
As other have said, be wary of insulating roof joists
Edited by satans worm on Monday 1st June 08:42
I should be ok with ventilation as I am not boarding everywhere, basically a 2m strip down the middle (its 2.16 wide) then the same 2m strip either side (they are 2.2m wide) and there is an air brick in the end gable.
I was going to cut down the 2.4m to be 2m to fit down the middle, eve height is over 2m so they should go in ok. the 400mm centres was so I could use the 370mm wide 150mm deep BOGOF Insulation offer at Wickes.
It is a early 70's build, but the internal walls on both floors are block work so I was not to worried about the additional weight, should I be?
Thanks, V.
I was going to cut down the 2.4m to be 2m to fit down the middle, eve height is over 2m so they should go in ok. the 400mm centres was so I could use the 370mm wide 150mm deep BOGOF Insulation offer at Wickes.
It is a early 70's build, but the internal walls on both floors are block work so I was not to worried about the additional weight, should I be?
Thanks, V.
Sam_68 said:
I won't bore you with the technical details, but basically these roofs are not designed to take the heavy loads from storage on the ceiling.
I went in one the other day where some underfloor heating 'specialists' had been in and they had notched the bottom member of the roof trusses about 30mm deep in various places......No problem as you've got blockwork below. You wont have a problem with damp as long as you dont block any ventilation, ie eves and air bricks etc. Boarded out one of my propertys using the method i suggested quite some years ago and has not given a hint of damp, no real reason it should.
sleep envy said:
it's going to be a warm job, I don't envy you
I was up in my loft yesterday fitting a shelf and it was more than tropical - a few minutes at a time was enough. In fact I do wonder about the heat being suitable for the stuff I keep there. Is there a quick and cheap way to add ventilation to a loft - some sort of vent just to get the worst of the heat out, or will it simply let in birds and other undesirables? VEX said:
It is a early 70's build, but the internal walls on both floors are block work so I was not to worried about the additional weight, should I be?
Yes, potentially.Trussed rafter roofs work to some extent like triangulated space frames in racing cars; the idea is that the ceiling tie members and bracing struts are all in pure compression or tension, not under bending loads.
Also, and importantly, they're joined together with devices called 'gang nails', which are basically plates with teeth stamped out of them. These gang nail plates are directional... their strength is dependent upon the angle of the load in relation to the gang-nail (and the way the gang nail is loaded in relation to the grain of the wood). If you load the ceiling in such a way that the direction of the loads in the truss are changed, the stiffness of the whole roof structure can be dramatically reduced.
If its a Fink truss (W-braced) trussed rafter roof, it spans from wallplate to wallplate. The internal walls may be blockwork for a different reason (buttressing the external walls, noise reduction), but they're not there to support the ceiling ties on the trusses and, indeed, the trusses should not bear significantly upon them.
Now, the building industry being what it is, we tend to use fairly high factors of safety (it's a house, not a Lotus racing car, after all), so you'll probably get away with it, but it's really not a good idea.
Thanks Sam,
So the idea of using the Kingspan insulted board stuff is better if a little more expensive. In theory it will reduce the weight and stress on the trusses as I will be removing the need for the additional joists and laid onto the existing trusses?
I'll just have to cut it down to widths that will go through the hatch.
Thanks
So the idea of using the Kingspan insulted board stuff is better if a little more expensive. In theory it will reduce the weight and stress on the trusses as I will be removing the need for the additional joists and laid onto the existing trusses?
I'll just have to cut it down to widths that will go through the hatch.
Thanks
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