Flat roof penetrations - how big is enough cables/AC

[Adam2]

Am about to finish the flat roof!!! Need a few holes:

 

1) 1 x svp

2) 1 (or more) for: aerial cable, future solar panel cable, possible future air con pipe/cable

 

My question is - would a 100mm one like below be sufficient for item 2?

 

I was thinking to put a large block of PIR into each end to minimise air leaks - not sure how perfect that can be though. 

 

Is there a better/simpler way to do this?

 

 

 

[TonyT]

You may struggle to get air con-2 copper pipes /fully insulated through 1 penetration.

 

but 2 of these with 1 air con pipe in each and split the cables would work.

 

can they not come out the wall?

[Temp]

+1  bring them out under the eaves/overhang or through wall if you can. 

 

 

 

[Adam2]

6 minutes ago, TonyT said:

can they not come out the wall?

Will have a think about that - much shorter route straight up for AC pipes.

 

I know zero about AC pipes - if copper then is it feasible/sensible to pre-install pipes and cap them off at each end at this stage to make life easier? or have a de-mountable u bend so the pipe bending can happen later on? Was thinking to have the pipe from a wall cavity behind a dressing room cupboard go straight up through the roof.

[TonyT]

it’s feasible, but there is also cabling between the indoor/outdoor unit too.

mot will need pressure tested and capped off, 

 

best to make sure a route from a to b is available with accessible risers/ underfloor ducts etc

 

 

 

 

[markocosic]

AC...

 

AC pipework typically goes through a 70 mm diameter hole ... including the drain pipe and the insulation and the cables etc

 

It'll either be 1/4" and 3/8" (mine is .. and runs through an old silicone sealant tube through the wall along with drain and cable) or 3/8" and 1/2" depending on size.

 

Insulation is about 15 mm thick and soft.

 

100 mm you could almost throw it through. ?

 

Buy from the likes of Saturn air sales if you want to preinstall. Leave oodles of slack. Flare some brake fittings and bleed nipples onto it for closing it off. Or pinch shut/bash flat, fold over on itself, and seal with a blob of solder. Don't get flux inside it.

 

1.5 mm x4 core more than enough for most ac units. (most power tends to be supplied to the outdoor unit, with only a little power needed by indoor unit)

 

Throw 5 core 2.5 mm SWA up and out to cover all possible scenarios...or just a good bit of UV resistant rope/galv fencing/draw wire. (most rope dissolves in UV by the time you get roundtuit)

 

 

[tonyshouse]

Never penetrate a flat roof, it will leak, actually all flat roofs are destined to leak

[makie]

30 minutes ago, tonyshouse said:

Never penetrate a flat roof, it will leak, actually all flat roofs are destined to leak

 

Not if done and maintained correctly.....

[Adam2]

Many thanks @markocosic most helpful. I've gone and bought a couple of swan neck penetrations kits which seem well made, if expensive for some moulded plastic. seems like that will be more than enough.

 

They are demountable so for now I can install this with a duct running down to a service cupboard and a drawstring taped inside for later use. Will cut some sections of PIR to fill in the tubes to avoid ventilation losses etc in the meantime. Will check with my electrician as mentioned earlier re cable prep to ensure safety/compliance.

 

The detailing on the single ply seems to be excellent and they can install a well made section to cover this and weld it to the existing membrane so although penetrations are not ideal I'm OK with this based on what I've seen so far