Extra insulation round SVP’s in a Kore passive slab?

[Gibdog]

Hello, 

 

We’re doing an MBC passivehouse (slab too). Our PH consultant has said we need to wrap the SVP’s within the slab in 25mm armaflex tuff coat - up to the slab seal. I.e. within the concrete.

 

MBC and Groundworks team say they’ve never done this before.

 

Have any of you guys?! 

[Russell griffiths]

You normally wrap the pipes in a 15-20mm thick layer of foam held in place with gaffa tape. 
this is usually to allow a bit of wiggle room around the pipe so it isn’t totally trapped by the concrete, this can help if having to add another joiner to the pipe as the joining collar can go down lower without hitting the concrete. 
 

if he’s worried about cold bridging, then he’s getting you to spend £20 to save 50p. Lunatic. !!

[Gibdog]

Thanks @Russell griffiths yes, his concern is thermal bridging - he admitted it’s small but as there are a lot of them they add up (we have 7 x 110mm pipes).

[Russell griffiths]

6 minutes ago, Gibdog said:

Thanks @Russell griffiths yes, his concern is thermal bridging - he admitted it’s small but as there are a lot of them they add up (we have 7 x 110mm pipes).

He’s a lunatic. 
why not block all your windows up then you wont have that problem either. 
we all want to build better, but you need to draw a line somewhere. 
 

if you are using the MBC double stud wall system and their insulated slab then you are splitting hairs, you will struggle to find a better system that works so well together. 

[Gus Potter]

36 minutes ago, Russell griffiths said:

He’s a lunatic.

Agree. Use a flexible exanding foam AFTER you have got the pipes finally positioned. Sometimes we have to have pops up really close to the raft slab edge so we need to make sure we can weave that though the main rebar, especially if we have point loads from Oak frames or the like.

 

Anyway an MBC type raft sits above the main insulation layer so it's on the warm side anyway.

[Gibdog]

Thanks guys, that’s great to hear - was going to be a real headache trying to get it for Monday/Tuesday. Once the slab is in, he’s said we need an airtight collar to seal the SVP to the concrete and then the rest of the stack can be constructed and insulated. Does that sound right too?! Any tips on products/materials for that part?  

 

[Nickfromwales]

9 minutes ago, Gibdog said:

Thanks guys, that’s great to hear - was going to be a real headache trying to get it for Monday/Tuesday. Once the slab is in, he’s said we need an airtight collar to seal the SVP to the concrete and then the rest of the stack can be constructed and insulated. Does that sound right too?! Any tips on products/materials for that part?  

 

LINK

 

You will also need to use a primer for the concrete, before wasting one of these grommets and finding out the expensive way. This is only recommended in acceptance of the fact that your man is waaaaaaaaaaaaaaaaaay OTT. A good frame sealant etc will suffice here tbh, but best to be a good boy and do as one is asked..

Give the concrete a good scrub with a hand brush and then give a squirt of this, being careful not to be wasteful.

LINK

 

9 minutes ago, Gibdog said:

and insulated

This is usually just for noise, so some Knauf acoustic mineral wool (rockwool etc) usually gets stuffed around the pipe at 100mm thickness to prevent the noise of flushed water creating nuisance noise to the room.

[Russell griffiths]

Tube of cheap silicon from screw fix £5 at the most, he is definitely a lunatic. 
do you need him anymore 

you have the slab booked in, mbc frame on top, guaranteed air test of 0.6, what more is he good for apart from costing you more money. 

[Nickfromwales]

3 minutes ago, Russell griffiths said:

Tube of cheap silicon from screw fix £5 at the most

Bruce, CT1 ffs, silicone is naff on a good day. 

[Nick Laslett]

On 14/03/2025 at 20:15, Gibdog said:

Thanks @Russell griffiths yes, his concern is thermal bridging - he admitted it’s small but as there are a lot of them they add up (we have 7 x 110mm pipes).

 

Here is the PHPP thermal heat loss paper on the topic for anybody that is interested. This paper might not address these specific circumstances, and there might be one that is more applicable, not a rabbit hole I need to go down.

 

https://www.elementalsolutions.co.uk/wp-content/uploads/2012/08/Heat-loss-via-internal-drainage-vent-pipes-full.pdf

 

I might get a placard made up, so visitor's know that I most definitely don't have Phassive House Certification and saved 10's of thousands of ££££ on nonsense costs.

 

When the revolution comes, I would be conflicted who to shoot first, Architects, Planning Officers, Buildings Controls, or now PHPP consultants. All said in jest, no harm meant, of course my build is full of passive house certified materials, plenty of intello membranes, nonsense £20 grommets, Siga tape, the list goes on. And the SVP stacks are all insulated with Tecsound FT55 AL Acoustic Pipe Wrap because the noise is a way bigger concern than a trivial heat loss.

 

[Gibdog]

Thanks chaps,

I'd read that heat loss paper a while back but good to be reminded @Nick Laslett

If we were to have to insulate (for thermal reasons) the stacks - would it therefore just be the one that goes outside, rather than the ones with AAV's? 

[Nick Laslett]

@Gibdog, whether they are venting outside or have an AAV, they need some sound insulation. This will also provide thermal insulation, but it is the sound you really want to address. 
 

This is a good thread from the old days of BuildHub on this topic. 
 

You might have already seen this thread.
 

 

NHBC is always worth a visit for minimum expected standards. 
 

https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/8.1/soundproofing-to-soil-and-vent-pipes-new-june-2020.pdf

As others have mentioned earlier in the thread, the thermal bridging is trivial, but you have to do what is required if you want PH certification. 
 

Good luck with your pour today and tomorrow. Getting out of the ground is a big milestone. Enjoy the process.  

Edited March 17 by Nick Laslett