Insulating over hips in loft bathroom?

[Ian H]

if I overboard the rafters with 50mm PIR my hips will stick out into the room.

It's going to be a bathroom so I'd rather cover the hips.

How would you do it?

Thanks.

 

[catlad]

Why not glue another layer of insulation to the walls to make up the difference.

 

[catlad]

If 50mm isn't enough then you could use insulated
plasterboard and cut back the insulation where it
meets the hip.

 

[freddiemercurystwin]

I would have say a 200 wide flat portion of say 25mm insulation + PB as you would do to under a ridge beam in a vaulted ceiling setup.

 

[Doggit]

You either need to build the rafters out so that they match the ridge, or as Freddie suggest, you put a board over the ridges till it touches the walls either side.

 

[Ian H]

I think I'll go with either Freddys idea of going accross the hips diagonally or maybe add a 100mm insulation to the side slope and see if that will cover them.

 

[^woody^]

if I overboard the rafters with 50mm PIR my hips will stick out into the room.

Try 60mm

 

[John D v2.0]

Whatever you do you're really going to have to fill the space with insulation, as having a good in your insulation layer is bad practice for condensation and bypass reasons.

 

[garyo]

my hips will stick out into the room.

I have the opposite problem with my valleys, and in my case it eats in to some head height in a door way so I'd like to minimise depth of cladding.

My understanding is that wood is actually a surprisingly good insulator when you're talking about a 300mm depth, so is there actually much of a condensation risk in just foaming plasterboard directly on to it?

 

[John D v2.0]

There are two condensation risks, one on the surface of the material which causes black mould, other other is interstitial condensation which happens in voids within the buildup.
For the former, there is a "limiting u value" for ceilings quoted in the building regs, which means that there won't be surface condensing in normal situation. As a result of the limit, it's normal practice to over board with a thin layer of celotex.
The op could calculate the u value at that crisp junction and see if it's safe to board directly.

 

[garyo]

How would you do it?

Also, I think your current approach is working well : cover the floor with so much cr*p that no one notices that the hip is sticking out!

 

[Ian H]

The op could calculate the u value at that crisp junction and see if it's safe to board directly.

He isn't that clever It's got 75mm between the rafters which I cut with (I think they call it) a 'compound mitre plumb cut' so it fitted tight and parallel with the hip, then I foamed it.

I'll see what thinkness I need to cover it and see how that affects the room. I dealt I want as thin as possible insulation on the right because that affects the door too.

 

[Ian H]

Also, I think your current approach is working well : cover the floor with so much cr*p that no one notices that the hip is sticking out!

What a good idea!!! She won't be able to fit a bathroom if it's ful of ****el!!

 

[John D v2.0]

He isn't that clever It's got 75mm between the rafters which I cut with (I think they call it) a 'compound mitre plumb cut' so it fitted tight and parallel with the hip, then I foamed it.

I'll see what thinkness I need to cover it and see how that affects the room. I dealt I want as thin as possible insulation on the right because that affects the door too.

No idea where crisp came from! I meant critical.
And I mean the u value of the wood as that's worse than the insulation. So find out wood thermal conductance in w/m/k then divide by 0.3m if that's the thickness, then that gives you the u value. If that's a smaller number than the limiting u value you're ok, if not you should insulate. The limiting u value is in the approved doc for insulation thermal.

 

[catlad]

Just don't use normal plasterboard in a bathroom
which ever way you approach it.