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recoveringacademic

Woke up in a cold sweat: underboarding too early?

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Our roof design has 200mm insulation between rafters and 80mm underneath. With only a little bit of cursing  and swearing I got three 80mm insulation boards up -on my own- yesterday. Vaulted roof spaces look sexy but they are sods to underboard.

 

0300 this morning : bububugger - I bet I should have put the studding in first - because that needs to be attached to the bottom of the rafters. And I've gone and hidden them now. Well, not quite. I can see where the rafters are because of the attachment points for the insulation. Those massive washers are a bit of a giveaway.

 

Am I going to have to dig out the insulation where the verticals meet the rafters, or should I put the studding in first - and then underboard?

 

Phhhh, 'nother steep learning curve I got myslef into innit? 

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Just doing this job in my shed right now....... I put the studs in first, insulted all of that and boarded the low stud wall, the top of my boards were cut at 45 degrees ready for me to slot the ceiling osb straight into ( this is a room in the roof so low 1m stud walls) like you I am working solo at the moment and having the pre cut board in place makes it so much easier. Your going to have a bit of a job cutting out the insulation for each stud..... are they 400 or 600 spacing ? Decide what’s going to be quicker and do that. I have 100mm of insulation over my studs and 60mm over my vaulted rafters, but will be sticking on another 25mm...... i had a bunch of 60mm for free so wanted to use it ! 

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5 minutes ago, Cpd said:

[...]

Decide what’s going to be quicker and do that.

[...]

 

In other words it's reasonable to do either;

  • put the studding in first then insulate under the rafters and round the studs  OR
  • underboard all the rafters and then dig out where the studs meet the rafters

Right?

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Fit a 4x2 head wherever the studwork will be onto the rafters then board either side of it. Quicker to work around a ceiling than with walls in the way.

 

You could also swap your timber for metal stud at that point too if you wanted. 

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2 minutes ago, PeterW said:

Fit a 4x2 head wherever the studwork will be onto the rafters [...]

 

Cheers lad....

The idea of metal studs is attractive, but I have a bit more confidence with wood. Maybe next house......

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You could fix head through insulation with long screws. How big is this stud

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I know it’s not the same as yours, yours will be a “ right proper job” but this is the way I am doing it in the shed. It’s a bit tatty but all the insulation was free as was the chipboard flooring on the walls, as were the windows etc etc...... 

FEB4D63F-D8BD-423D-AEB1-55C8BAFC8A69.jpeg

72997817-9B0E-4BF0-98C8-D6B9768C7A64.jpeg

AA3429B0-821D-4C87-8C66-8757B13D6925.jpeg

FD412608-5F02-428D-A876-17731B334A8C.jpeg

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55 minutes ago, Oz07 said:

You could fix head through insulation with long screws. How big is this stud

 

Erm, 'normal'.....

If you mean height, it'll be just under 3.0 meters

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37 minutes ago, Cpd said:

I know it’s not the same as yours, yours will be a “ right proper job” but this is the way I am doing it in the shed. It’s a bit tatty but all the insulation was free as was the chipboard flooring on the walls, as were the windows etc etc...... 

 

Well, for free stuff, that looks excellent.

So, those screws go through the  board, through the Celotex and into the joists / rafter?

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33 minutes ago, recoveringacademic said:

So, those screws go through the  board, through the Celotex and into the joists / rafter?

Yes they are 150mm with big heads so you can really tighten them down, some need to be countersunk to give them a bit more depth  as your only left with 30mm to grip into the wood, seems to work well though. Bigger screws would be better but that’s all I had in “stock” the ceiling is easier as it’s just 60mm with about 11mm osb so 90mm  fixings work fine as there is more flex in the insulation and osb... again 100mm would be better but it’s just my shed and trying to use up what Ive got laying  around. No point getting all this stuff for free and not  using it one way or the other. 

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My plan's about the same as @Oz07's: JJI rafters with mineral wool between, VCL, underboarded with 90mm PUR, battened service void then cladding appropriate to the area (OSB, plasterboard or wood). Battens screwed through PUR and VLC to rafters. PUR will be a continuous layer, not stopping at room partitions.

 

Where the internal walls meet the roof I'll substitute CLS for the battens and use somewhat beefier screws through to the rafters. But, mine's an A-frame over post-and-beam so most of the stud walls which meet the roof will only be small triangles outboard of the posts so won't be subject to much force.

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generally internal partitions go up after the ceiling is finished, so you would fit your underboarding, brandering @400 centres including dwangs to catch partitions, plasterboard ceiling then erect your partitions the only partitions that should attach directly to the structure are structural ones which should already be fitted, there is no point in adding 80mm insulation and then cut massive holes out of it for all your partitions as you are just adding lots of cold bridges

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