Insulating a bathroom - waste pipes thermal bridge?

Submitted by lyoshav t3_10dlv87 in DIY

I'm fitting some insulated plasterboard to the inside of the exterior walls of my bathroom, taking care with the joins with windows. But it strikes me that the waste pipes from the toilet and basin - which go out the wall and down the outside of the house - create two great big thermal bridges with the outside.

I've searched the web and not found anything addressing if there's anything worthwhile to be done about this. Lots of stuff on insulating pipes to avoid freezing but that's not a problem here. I'm doubtful that it's worth it from an energy efficiency pov.

Any advice/thoughts?

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upkeepdavid t1_j4mbmeh wrote

This is exactly what engineers do ,find Solutions to problems that don’t exist

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redcore4 t1_j4m1ei6 wrote

Aren't waste pipes mostly empty apart from the water in the S bend? There'll be no direct air movement from outside to in because of the S bend, and the water movement will always be in the one direction (taking warm out, but not bringing cold in), so it doesn't seem to me like there's an issue here.

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lyoshav OP t1_j4m5jew wrote

No air movement, no, but the pipe material itself and the air inside (not moving) must create a thermal bridge with a significantly worse u value than the walls. I'm wondering what one does able this, if anything, if going for the full enerphit treatment...

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redcore4 t1_j4m67p7 wrote

The loss will be fairly negligible compared to the cost of preventing it as plastic pipes don't conduct heat well and neither does still air; but if you want to invest in removing even that tiny little bit you could box in the pipes on the outside with insulated ducting. The expense probably wouldn't be worth it though.

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MidnightAdventurer t1_j4n0h9d wrote

The pipe material is usually PVC? PVC doesn't exactly transmit heat very well, in fact, it's one of the materials used to improve the thermal properties of window joinery. Neither does terracotta if you've got pipes that old but they're not usually used above ground.

The only pipe materials you're going to have a problem with creating thermal bridges are metal and for a waste pipe, that probably means cast iron. If your house has cast iron waste pipes then there may be some thermal efficiency benefit to replacing them with PVC, otherwise the pipe material is basically an insulator.

The air in the pipe will generally match with the outside air whatever you do because pipes are vented (don't block the vents...) but air isn't much of a conductor of heat either - the biggest problem with air when insulating is letting the inside air escape and be replaced by outside air. This is easily managed by sealing around the pipe where it goes through the wall.

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lyoshav OP t1_j4n3kdn wrote

Thanks, interesting and helpful.

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