Newbie MVHR / PIV Question. Is it worth the outlay?

[Dean Mc]

Hi,

 

I have another rookie Q for anyone who may be able to help?

 

We’re about to build a house using ICF but the majority of areas, all bar the bedrooms and bathroom, will have vaulted ceilings. Our drawings have been submitted to our LABC and list MVHR, but we hadn't requested this be added, only discussed the potential.

 

The primary heating will be ASHP with wet underfloor heating, with a wood burner but mostly just for effect.

 

We’re down in Cornwall and I’m a little concerned about damp, having lived in many properties down here which have suffered from it. However, I don’t know whether this will be an issue with our building, or whether MVHR / PIV is the correct solution.

 

Some people have mentioned MVHR and PIV, but;

i. Is MVHR of any benefit or required given it’s an ICF house with ASHP?

ii. Can this be done effectively with a mixture of ceiling types but mostly vaulted?

iii. Do the benefits outweigh the costs, as we’re on a very tight budget?

 

So, we're trying to ascertain whether we change the build regs application back to without MVHR or keep it with and take on the additional costs?

[eandg]

Given ICF is inherently airtight then you will need MVHR to ventilate the house and get rid of moisture, I'd have thought. 

[ProDave]

Forget worries about damp.  ICF is a good build method, just go ahead and fit MVHR and you will have a very good damp free house.

[Dean Mc]

Thanks both. 
 

can it still be fitted without roof / loft voids ?

Edited December 11, 2022 by Dean Mc

[Radian]

12 minutes ago, Dean Mc said:

can it still be fitted without roof / loft voids ?

Sure. Do you have a plant room with an outside wall?

[Adsibob]

1 hour ago, Radian said:

Sure. Do you have a plant room with an outside wall?

I think @Dean Mc is more concerned about how to conceal the ducts given he has few void spaces.

[Dean Mc]

We do have a plant room with an external wall, but adsibob is right, in that how could it all be physically installed and concealed, switching between vaulted and conventional ceilings?  

[Bonner]

Is it single or two storey? How are the other services being routed? You may need to create some service voids. Might be worth posting the floor plan to get some suggestions what to do. Highly recommend you do fit some kind of ventilation system by the way!

[Simon R]

9 hours ago, Dean Mc said:

Some people have mentioned MVHR and PIV, but;

i. Is MVHR of any benefit or required given it’s an ICF house with ASHP?

ii. Can this be done effectively with a mixture of ceiling types but mostly vaulted?

iii. Do the benefits outweigh the costs, as we’re on a very tight budget?

Hi,

first damp should not be a problem, we have the opposite problem and now have lots of house plants to keep teh humidity at comfortable levels.

We did our build with ICF and put a fair bit of planning into reducing heat loss, to the extent that we had no need for a heat pump. By not having a heat pump and underfloor heating it save a lot on costs. If you use an insulated raft the floor is at room temperature anyway.

1. MVHR is essential, we have vaulted ceilings and it took a bit of head scratching to work our our best ducting options.
2. Yes
3. Yes

We did our build on a very tight budget and you can build an very comfortable home with very low running costs for not a lot of money, especially if you can do some of the work yourself.

We did a blog of the build which you may find useful as it sounds as though your build may be similar to ours.

 

[SteamyTea]

9 hours ago, Dean Mc said:

We’re down in Cornwall and I’m a little concerned about damp

Welcome

 

So am I, I don't think damp is a Cornish problem, crap housing stock is though.

As other have said, you really need MVHR, just a matter of designing it in from the start.

As you are having UFH, what floor U-Value are you designing to?

 

ICF seems popular down here at the moment, we did have a member that was working for a local company, but he seems to have vanished.  Can't remember who it was now.

[Radian]

8 hours ago, Adsibob said:

I think @Dean Mc is more concerned about how to conceal the ducts given he has few void spaces.

Start at the bottom and work up 🙃

Depends on whether we're looking at a cold roof or warm roof, vaulted ceilings can also be difficult to get right from the POV of insulation especially if there's a big steel ridge beam. We've seen this a few times here. Whatever work-around is found to remove the cold bridge could include ducting/vents.

[Conor]

Our first floor is all vaulted. We formed two service voids, each going up through the two bathrooms for the soil ipes, but continued they on up to the ceiling for the 6 ventilation ducts. We then simply have a shallow dropped ceiling under the ridge (ridge steels need to be boxed in anyway) that gives us the space for ducts and plenums. Still ahve 3m+ ceilings, just the ridges flattened off.

 

MVHR is essential in an ICF build. We had walls dripping with condensation before we got ours up and running. Humidity now a thing of the past.

[jack]

Any reason you can't install inlets and outlets high up on a wall instead of in the ceiling?

 

Alternatively, all of our upstairs outlets (bedrooms) are in the floor, with ducting run through the posi-joists underneath the floor. Extracts in the bathrooms are in the ceilings, but could have been installed high up on the wall if that hadn't been an option for some reason.

[Dean Mc]

Sorry, should have mentioned, build is single story in the shape of a T. Bedrooms and bathroom in one limb across the top with the master bedroom at the end and en-suite vaulted. Open plan kitchen, dining room and lounge running north to south at the bottom part of the T, which are vaulted throughout. 

[SteamyTea]

4 hours ago, Dean Mc said:

shape of a T

You could look at dMVHR.

Basically though the wall extractors with heat recovery.

May need two, and a cooker hood  in the kitchen, lounge, diner.

 

Have you considered summer cooling? This could change the whole ventilation design somewhat. Not that it is really needed down in the SW. the sea keeps the temperatures suppressed.

[JamesP]

Our MVHR supplier provided a unit based on the floor area of our new build, not the volume and with many vaulted and high ceilings really did 

not meet the requirements to pass building regs.

However a solution was found to satisfy building control and it works fine.

 

[JohnMo]

Some light reading

Atamate_SDAR+Paper+2019+(1).pdf

 

On MVHR, we used posi rafters and strung the pipes through the gaps. We also made good use of coanda effect terminals.

[Buzz]

20 hours ago, Dean Mc said:

can it still be fitted without roof / loft voids ?

This is what I ended up doing , the void is lower than it needed to be but looked right for the room.

[Dean Mc]

On 12/12/2022 at 18:20, JohnMo said:

On 12/12/2022 at 18:20, JohnMo said:

Some light reading

Atamate_SDAR+Paper+2019+(1).pdf 2.47 MB · 11 downloads

 

On MVHR, we used posi rafters and strung the pipes through the gaps. We also made good use of coanda effect terminals.

 

On 12/12/2022 at 19:08, Buzz said:

This is what I ended up doing , the void is lower than it needed to be but looked right for the room.

 

Thanks JohnMo, I'll have a flick through.

 

Hey Buzz, thank you. Are you still WIP or do you have any images of it all boarded and covers fitted?

 

[Buzz]

45 minutes ago, Dean Mc said:

Hey Buzz, thank you. Are you still WIP or do you have any images of it all boarded and covers fitted?

Not got around to fitting the covers yet. 

[Dean Mc]

That looks perfect. Would be interested to see with covers on. One of my concerns is that as the vaulted ceilings are a feature, putting extra covers and fittings on there may have spoiled the affect.