SVP through insulated roof (passiv house)

[junglejim]

Hi, I’m looking for the best route/method to install the svp. My understanding is that it needs to be 3m from a window opening so will need to go between rafters and exit the roof near the ridge. The roof construction is osb, rafters with rigid insulation between rafters then osb beneath rafters And another layer of insulation. Cutting through this to install an svp feels counter intuitive and could introduce cold bridging… does anyone have any advice in the best way to install, products etc to maintain thermal efficiency.

 

 Thanks

Edited Thursday at 20:25 by junglejim

[Conor]

Install an internal air admittance valve instead. We've three stacks in our house, each one with an AAV. No need for an externally vented stack.

[junglejim]

20 minutes ago, Conor said:

Install an internal air admittance valve instead. We've three stacks in our house, each one with an AAV. No need for an externally vented stack.

Thanks Conor, that’s interesting. I mentioned that to a plumber who said bc would need external vented svp… do you know where I can find more info about this? 

[Conor]

3 minutes ago, junglejim said:

Thanks Conor, that’s interesting. I mentioned that to a plumber who said bc would need external vented svp… do you know where I can find more info about this? 

Nope, no requirement under BC regs for this. Old school thinking from your plumber. Save yourself a bit of money, hassle, and a compromised building fabric and go with the AAV. Read up the building control regs relevant section (a Google search should get you this) and you'll see that it specifies adequate means of air admittance. I'm in NI but our regs are basically a copy and paste of the English ones. Scotland is different tho 

Edited Thursday at 21:08 by Conor

[tuftythesquirrel]

Hi @junglejim, 
There is no need to do this. It's an old-fashioned approach, and the last thing you would want to do is stick a great big "thermal bridge/ cooling tube" through your insulation layer. I had the same issue and found Jeremy's post below. (Subject - Air admittance valve / soil vent pipe). He clearly explains the reasoning and how to implement it.He clearly explains the reasoning and how to implement it, using AAV's.

 

https://forum.buildhub.org.uk/topic/4459-air-admittance-valve-soil-vent-pipe/

 

[ProDave]

1 hour ago, Conor said:

Nope, no requirement under BC regs for this. Old school thinking from your plumber. Save yourself a bit of money, hassle, and a compromised building fabric and go with the AAV. Read up the building control regs relevant section (a Google search should get you this) and you'll see that it specifies adequate means of air admittance. I'm in NI but our regs are basically a copy and paste of the English ones. Scotland is different tho 

Not entirely as simple as that unfortunately.  So worth checking with your BCO what they want.

 

In my case BC insist that the drain run be vented at both ends, it is vented in the treatment plant, and they insist the other end has a real actual vent pipe.  Now because I did not realise this, I had not provisioned for one, so I was not allowed to fit an AAV to the top of my main stack pipe.

 

I could have done that, if only I had known of the need to vent the end of the drain run.  I could have run a pipe up the outside of the end wall of the house to achieve that, and then I could have used an AAV inside the house.  Unfortunately by the time I realised this my driveway was concreted so it would have meant digging that up.

[Iceverge]

No mains sewerage here so on a domestic treatment tank. 

 

Our AAV is working perfectly so far.

 

We have a vent stack that runs up the back of the garage.

[junglejim]

Thank you for all of the advice so far.

i don’t know if this complicates it at all but also worth noting that our sewage and grey water will go to a small pumping chamber sink in the drive which in turn pumps to the main sewer.

@Iceverge @ProDave @tuftythesquirrel @Conor

Edited Friday at 08:38 by junglejim

[Thorfun]

our BCO insisted on a SVP. managed to reduce the visual impact with a slate vent

[Mike]

14 hours ago, Conor said:

Save yourself a bit of money, hassle, and a compromised building fabric and go with the AAV. Read up the building control regs relevant section (a Google search should get you this) and you'll see that it specifies adequate means of air admittance

Always a good idea if you can. However, at least in England & Wales, it is necessary for sewers to be vented to the open air in places so that the sewer gasses - which are toxic and can be explosive - can safely escape. That's normally required at the head of the sewer run, and every few properties (often 5) along the way. That is covered by Part H of the Building Regs, section 1.33:

 

Ventilated discharge stacks may be terminated inside a building when fitted with air admittance valves complying with BS EN 12380:2002. Where these valves are used they should not adversely affect the amount of
ventilation necessary for the below ground system which is normally provided by open stacks of the sanitary pipework.

 

If you are required to have an open stack, there are a couple things that you could consider. One possibility, if you're not more than 2 stories high, is reducing the pipe diameter to 75mm diameter(Section 1.32). Another, if you have a nearby detached garage, is to extend the sewer to that, then run the vent pipe out of the garage roof. And, as @Thorfun suggests, it's normally possible to hide top of the pipe with a vent tile.