MVHR Loft Installation - Inspiration

[Redbeard]

@Mr Punter, as I read it I think that when @richo106 says 'over the top' it means 'underneath', as the next things are VCL and plasterboard. @richo106, can you confirm? 

[richo106]

5 minutes ago, Redbeard said:

@Mr Punter, as I read it I think that when @richo106 says 'over the top' it means 'underneath', as the next things are VCL and plasterboard. @richo106, can you confirm? 

Yes my apologies for any confusion, I meant 50mm under the rafters.

[richo106]

20 minutes ago, Iceverge said:

It might help if you posted full section drawings of what is proposed so far. It sounds like you may have some insulation on slope as is buy it's unlikely to be a warm roof. 

 

You may want to blank out any personal details. 

 

Good news is that you're somewhat ahead of the curve here. Budget wise you'd be advised to get a hold of things as soon as possible and start designing out some expense now if you can. 

 

 

 

 

 

 

 

Regarding sectional drawings I haven’t got any, only drawings I have are architects drawing and structural engineers drawing no specific insulation levels.

 

regarding designing out some expense, everything I do so far just seems to add cost so would be welcome to any items that could design out cost

 

[richo106]

I really done appreciate all the replies and time taken to reply!

 

I honestly have no idea where I would be without this forum so far

 

[Linto]

Here's a good resource for the different insulation roof types.

https://insulation-uk.com/roof-insulation/pitched-roofs by the sounds of it you'll want what they call pitched roof sarking but have a look at them all so you have a good idea of your options.

[Linto]

One thing to consider is that the sarking option may be cheaper than above & between or between & under due to their increased labour costs (it's time intensive to cut and fix the rigid boards between rafters). Lying them on top is quicker but needs more specialist fixings.

[joe90]

Well mine is a warm/hybrid roof so MVHR unit in the loft was easy. I hung the unit from the rafters, on rubber mounts so no vibration can enter the house/bedrooms. I only needed to insulate the external pipes (6” pipes from the unit to the outside). The other plus is the loft is great for storage at house temps and the loft hatch does not need to be airtight.

[Iceverge]

I've been thinking about this all day. All the above options are good but they will attract more cost unfortunately.  The more I look at this the more I'm unsure if the MVHR is the right option.  There's a section on the ground floor where you have 7 ducts crossing through a 225mm joist. 

 

 

 

 

Then what looks like 9 ducts passing through a steel beam. 

 

 

 

 

You're going to end up doing some serious boxing out here to get it all hidden, as well as a myriad of extra elbows in the ducts.

 

 

 

 

The main purpose of any ventilation system is to provide top quality indoor air. The MVHR adds the heat recovery part to save some energy. It's debateable if it actually saves any money given the cost of filters and initial outlay. 

 

Something like demand controlled ventilation or continuous extract ventilation would also mean high indoor air quality but would be much easier to plumb in. You need not go to the hassle of making the loft a warm space either. 

 

 

I would run 8 ducts from a central unit placed in the loft, 2 to the ground floor W/C, 2 to the kitchen, 2 to the ensuite and 2 to the bathroom via 8 port manifold in the loft and silencer.

 

 Times 1 X

 Times 4 X

 Times X 1

 

 Times X 1

 

A variable speed controller and some ducting, a few wall inlets and vents and you're home and dry. Probably less than £1000 and very simple to install by comparison. 

 

You could pair it to an ESHP like of these for about £2,500 and you'll get all then energy back you would have done from the MVHR as well as a COP of above 3 on your DHW heating. 

 

 

 

 

Also, something has been niggling me, airtightness hasn't been thoroughly planned in from the start. No great problem for 3 ACH maybe, but it does mean that you'll have lots of small holes. The big risk is moisture from the house finding it's way into the structure and causing rot. Running a continuous extract system would ensure that any small cracks only let air in from the outside and not visa versa by running the house at a slightly negative pressure. Any damp air is taken by the ventilation system and dumped safely outside. 

 

With diligent caulking (flexible caulk) around all penetrations you could probably avoid the need for airtightness membranes etc too. 

 

 

Have a think and I'd like to know what the collective thinks also. 

 

I have some other thoughts about the build too looking at the pic but one step at a time!!

 

 

 

 

[richo106]

Hi @Iceverge

 

Thank you for the reply, you are correct that air tightness hasn't been planned from the start. With the rise of energy costs and a few chats with friends kind of persuaded me to go down this route.

 

Regarding the ducts, i was planning on running the ducts passed the steel beam and into the kitchen area that way. This would cause them to take a slightly different route.

 

All day I have been thinking about this and if I am wrong to go with MVHR, i am going to email the guy I got it off and see if he does any returns policy at all.

 

I have measured up the roof area and i reckon there is around 114m2 of roof rafters that will need the insulation, and if i go with 120mm PIR & 50mm PIR it will cost the best part of £4500-£5000 just in materials

 

Would also like to hear the opinions of others

 

Regarding the other thoughts about the build, if you would like to private message me about this. I would very much like to hear your thoughts on this

 

Thanks again

 

[Linto]

Would a load of single room mvhr extractor fans work? Just have them in the areas that need the ventilation, bathrooms kitchen and maybe one or two communal areas? Be easier than running loads of pipe work through the steel. Plus maybe cheaper? 

But would obviously only be cheaper if you can return the already ordered stuff.

Edited January 10, 2023 by Linto

[richo106]

4 minutes ago, Linto said:

Would a load of single room mvhr extractor fans work? Just have them in the areas that need the ventilation, bathrooms kitchen and maybe one or two communal areas? Be easier than running loads of pipe work through the steel. Plus maybe cheaper? 

But would obviously only be cheaper if you can return the already ordered stuff.

This is my concern now that its very likely i won't be able to return any of it so going to have to make it work somehow

 

To keep the cost down of the warm roof could I use knauf insulation rafter roll 32 with 50mm PIR over the top? On their calculator this would be a U value of 0.13. Is this acceptable for a roof?

[richo106]

In an ideal world we would use the equipment we have on site, I keep going back to the idea suggested by @Redbeard and creating a MVHR house within the loft. This would only be extra cost of the additional insulation to surround this and a bit of stud work

 

And to negate all the ducts going through the cupboard i could stud out the wall in bedroom 2/dressing to take the pipes down to the ground floor and come out the correct side of the RSJ. Or run them straight across the hallway and into the kitchen missing the RSJ

 

If I have air layer on my first floor ceiling could this potentially work?

 

 

[richo106]

Tempted to remove the velux window over the en-suite so I can build the "MVHR house" off the bedroom vaulted ceiling wall. Not sure how happy the mrs would be about that

[richo106]

Update:

 

I have spoken to guy who I got the MVHR system from and they don’t offer any sort of refund which I expected. It seemed to be a hasty decision to purchase it but it’s done now.

 

Least I know I have to make it work 

 

I mentioned the installation issues that were raised and they said:

’The MVHR unit is insulated and can be installed into a cold roof, the 75mm ducting will need to run on top of the roof joist then rockwool can be poured over these pipes to hold the heat, at the moment I am seeing 300mm – 400mm’

 

 

[MJNewton]

Mine's in a cold loft and performs perfectly fine, and consistently over 80-90% efficiency. It was a retrofit to so much harder than a new build, but I'd happily do it all again (well, okay, happily might not be the right word to apply throughout but most of not all of that is down to the extra challenges of retrofitting). 

[richo106]

9 minutes ago, MJNewton said:

Mine's in a cold loft and performs perfectly fine, and consistently over 80-90% efficiency. It was a retrofit to so much harder than a new build, but I'd happily do it all again (well, okay, happily might not be the right word to apply throughout but most of not all of that is down to the extra challenges of retrofitting). 

That’s good to hear, I am happy to lay the insulation over the ducting and even the manifolds etc but my concern is the amount of holes I need to make through the FF ceiling which will greatly effect air tightness in my build 

[richo106]

Just now, richo106 said:

That’s good to hear, I am happy to lay the insulation over the ducting and even the manifolds etc but my concern is the amount of holes I need to make through the FF ceiling which will greatly effect air tightness in my build 

Would you be happy to share any pictures of your install in the loft? 

[MJNewton]

1 hour ago, richo106 said:

Would you be happy to share any pictures of your install in the loft? 

 

Sure! Anything in particular?

 

As a starter for ten, here's the 'bare bones' unit mounted and with the primary connections made:

 

 

 

 

 

[MJNewton]

(Tripped the file limit with the first pic so following on here)

 

And then more towards the end once the distribution pipework had been put in (4 extract and 8 supply if memory serves) along with insulation around everything:

 

[richo106]

Thank you @MJNewton

[john0wingnut]

Im working through the motions, planning my retrofit, which will go in the loft. Biggest problem for me currently is - I need a unit in the 400-500 m3/h range and most of them are bigger than my loft hatch, which is 500mm wide (1000mm length isnt a problem).

 

For the pipes off the unit I'm going to use something like this: https://heatpex.pl/en/new-insulated-mass-flow-duct-work/ or https://www.phstore.co.uk/zehnder-comfopipe/zehnder-comfopipe-plus as its already insulated, the later has 43mm of insulation.

 

Unit wise, I have been looking for ones purely made from EPP, to minimise the risk of condensation in the winter, however slim pickings from what I can find.

 

Still debating over whether all the radial ducting needs insulating too, although it will be under 300mm for glass wool.

 

[Iceverge]

On 10/01/2023 at 21:21, richo106 said:

Regarding the other thoughts about the build, if you would like to private message me about this. I would very much like to hear your thoughts on this

 

Nothing major,

 

Just that I noted PIR boards in the cavity. Expensive and tricky to get right. It looks like a 100mm cavity, I would consider switching to mineral wool full fill batts. Cheaper and they will work much closer to their design insulation value in reality. A parge coat and then insulated plasterboard would give you the required U value and help deal with some of the cold bridging inevitable with a renovation. 

 

 

[GraHal]

On 10/01/2023 at 12:08, Iceverge said:

 At 3 ACH the benefits of MVHR may be marginal 

I'm not doubting, just interested ... what is the reasoning behind the above statement?

Thank You 

[john0wingnut]

2 hours ago, GraHal said:

I'm not doubting, just interested ... what is the reasoning behind the above statement?

Thank You 

If you have a leaky house, you will be losing heat through air leakage and thus this is not recovered by MVHR