SBMS

How come all MVHr designers size off the volume of the house, not the number of occupants?

Thanks. Never really thought about from perspective of number of people in house. Family of four with 2 dogs so my gut is that although it’s a large house, something like the q600 would suffice. @JohnMo why did you go for two units out of interest (and how on earth did you get that for 2k!)

What would you aim for? I did do my heat loss calcs targeting 0.3ACH as it was a ‘healthy minimum’. I suppose this reduced the need for a larger unit even more?

So if the house volume was, say, 900m3 and I was aiming for 0.5ACH the unit would need to do 450m3? (Obviously would want to run it around 70% so probably would need 645m3?) when they do their sizing do they account for target ACH?

Not sure what you mean by over ventilation? Re your comment on price over 20 years, it’s not really the motivation for the MVHR. More because we are aiming for high air tightness so need MVHR and the comfort element.

Also - can anyone help with a very simple way to size a unit based on the size of the house? I see figures on the units like 600m3/h airflow and 108l/s requirement for building regs - how can I calculate the requirements for the house?

Currently looking at MVHR options for our build. Around 390m2 Over three floors (room in roof) so we have been given two options from BPC for MVHR: 2x Zehnder Q450 (total price 7901) 1x Komfovent r700 (total price 6000) same ducting for both options. The zehnder is 95% heat recovery but the komfovent is 83%. However I would prefer to only have a single unit and there is a price differential of 2k which I probably wouldn’t make up in heat recovery costs vs the equipment cost difference over lifetime of the unit. I also don’t know if electricity running costs would be greater with 2 units. Anyone been in a similar situation or have any advice as to which route to proceed?

Is your ‘airtightness membrane’ a VCL? I think I read the differential of the vapour resistivity between the inside (membrane) and outer (OSB sarking) needs to be around 5:1 to ensure vapour migrates out. It’s worth just checking this because if it’s at risk of condensation at least you know it’s down to makeup and not poor workmanship (design not build). Knowing doesn’t fix your problem though. I’m surprised that even with MVHR you still have a problem as that should help. I would suggest your nuclear option is to fit a dehumidifier and keep that running. You can get ones that are wall mounted and the condensate outlet can be plumbed in.

Where is your roofing membrane?? Should be under your counter battens/on top of your sarking boards?

Thanks - it’s all contained in the system itself as it’s effectively a swim spa. So filtration etc is done within the gubbins - like a massive hot tub. No separate pump room required. Heating is done via a supplied ASHP. Ventilation is not supplied and I need to look at a dehumidifier and vent system separately. Is that a single block wall basement that your pool was dropped into? how did you waterproof the basement area?

Getting my SE to design it and can then get it quoted up. Will report back!

Absolutely amazing result and fantastic news. Fair play to the other person that dealt with this. I bet your build just become a lot brighter! After that you’ll be able To deal with any issues that come up and think at least it wasn’t as bad as your last 24 hours!

Do you work for an inflatable pool company??

I think 90cm would feel a bit more like walking in a bath - I was thinking 140cm was pretty shallow. On site today and the groundworker has dug our foundations down to about 1100mm from DPC. The hole was dry as a bone at least…

Did you receive a full liability notice and was it in your name?

Unfortunately reading the above I think they did. They’re usually the first to respond on an application to let you know CIL is liable…

It’s a bonkers price per sqm @nod - £365. Think you’re up north like me where we pay around £65.

Who is your local authority?

The problem you’ve got is the CIL is due and the council will pursue matters against you. You’d be fighting on two fronts - one against the council and one against the architect… but a planning solicitor would help on both fronts and hopefully be able to look at whether the architect had any liability. Contact a solicitor tomorrow.

Fair point @joe90 if the contract called out all planning matters inclusive of CIL arrangement fair enough. If they did I’d definitely pursue them - their professional indemnity would pay out, result all round. Our RIBA stage/worded contract definitely didn’t. @Berkshire_selfbuid - what was your contract with your architect? Care to post it (anonymised)?

Firstly - how did they arrive at such an enormous figure? How big is your house and did they subtract existing floor space from your bungalow? OK.. some harsh words coming but bear with.. I completely empathise with your situation. Unfortunately this is a little bit of an ‘ignorance is no defence’ - certainly I don’t think there’s any point in pursuing your architect. They’re not really responsible for this (indeed ours had zero involvement in this process. Even our planning consultant bowed out at the end and I dealt with CIL directly for my exemption). it is an overly bureaucratic a process but councils are very very punitive with it. Self builders are an easy target because they don’t always know the exact sequencing. I would say it’s almost certain your LA will not waive it - especially such a large amount. They are, unfortunately legally entitled to demand this of you and why would they not? I’ve posted elsewhere that our local council pursued a widow for 30k on CIL because her husband died and he hadn’t put her name on the CIL. They asserted that ‘he’ hadn’t lived in the build for 3 years (because he had died from cancer I might add) and were collecting against his estate as they were legally entitled to do. Talk about the letter of the law vs the spirit.. That being said, you do have the option of pursuing this matter legally. With such a vast sum owed I would recommend you retain a solicitor specialising in planning law disputes (Ellis jones is one, there are others). You might have deeper pockets than the council (many are technically bankrupt) and they may not even want to risk their legal costs to defend an action from you. But with a large sum… they might. Speak to a number of planning dispute solicitors and get advice from all and see whether they think you have a case. Unfortunately I think that’s your only option.

Thanks @Russell griffiths I am 50/50 abandoning the idea but worry I might forever regret it. Someone on here gave an excellent argument by reasoning what was the cost per swim. Good way to look at it. Will come back here once I know more and have a price for it all.

Interested to hear how much it would cost you? Also.. you said you had two pools.. so the first must have been pretty good if you did it again??

Appreciate it @Russell griffiths we’ve designed it such that the pool room is effectively a single story flat roof extension connected to the house. Pool section would be at least 3m away from foundations of the main house. Have done this to try and minimise issues with affecting main house. I think my current route is to get a design from SE for the retaining wall and foundation design. Then I’ll get a waterproofing design done. Builder can quote from that and I can see if it’s worth doing or not. Can report back here if anyone is interested Appreciate some think it’s a crazy idea full stop… but Am I following a sensible plan there or missing anything?

Yes of course. Structural engineer will design retaining walls and impact on foundation design etc, it’s just that there wouldn’t be any load outwards from pool itself.