1st Floor HRV Duct Positioning

BarneyMc

Here's a quote I read recently in a Passive House magazine:

"...one common issue is HRV ducting being installed outside a building's thermal envelope. All supply and return ducting should be in a service cavity within the insulation and airtightness envelope of the building. At a minimum, the ducting should be at least within the insulation envelope."

In my two storey house I plan to position the HRV ducting for the first floor in the attic space on top of the joists, sandwiched between 2 layers of approx 300mm of insulation wool. The ducting will also have its own insulation covering.

Ignoring the penetration of the air-tightness membrane, does it really make much of a difference having it here compared with having it in a service area below the joists?

New Build 2015

BarneyMc wrote: »

Here's a quote I read recently in a Passive House magazine:

"...one common issue is HRV ducting being installed outside a building's thermal envelope. All supply and return ducting should be in a service cavity within the insulation and airtightness envelope of the building. At a minimum, the ducting should be at least within the insulation envelope."

In my two storey house I plan to position the HRV ducting for the first floor in the attic space on top of the joists, sandwiched between 2 layers of approx 300mm of insulation wool. The ducting will also have its own insulation covering.

Ignoring the penetration of the air-tightness membrane, does it really make much of a difference having it here compared with having it in a service area below the joists?

Interested to hear responses on this also

Rabbo

With the levels of insulation you are talking about, I wouldn't worry about it. The reality is that hrv ducting is often installed outside the insulation envelope, especially in upper floors.

One alternative is including the attic space within the thermal envelope and insulating up the rafters up to the ridge however this obviously adds to the space you are heating.

BarneyMc

I'll be having a cold attic so definately won't be insulating up the rafters. I guess it will be sandwiched between the mineral wool in the attic space plus have its own insulation wrap so the heat loss should be minimal?

mfceiling

Rabbo wrote: »

With the levels of insulation you are talking about, I wouldn't worry about it. The reality is that hrv ducting is often installed outside the insulation envelope, especially in upper floors.

One alternative is including the attic space within the thermal envelope and insulating up the rafters up to the ridge however this obviously adds to the space you are heating.

I'm seeing this more and more. Lots of houses that I did ceilings for last year requested a dropped ceiling upstairs also. Some of them had "warm roof" construction and kept as much pipework/hrv/electrics out of the roofspace as was possible.

ht9zni1gs28crp

Dropped ceilings seems to be working well on paper for me so far....

I aim to keep everything inside the insulation line and so resulting in as few penetrations of the Air tight line as possible, I think I have three areas in total that penetrate my air tight line in the whole house. Bar windows obviously!

BarneyMc

Bethany Breezy Jail wrote: »

Dropped ceilings seems to be working well on paper for me so far....

I aim to keep everything inside the insulation line and so resulting in as few penetrations of the Air tight line as possible, I think I have three areas in total that penetrate my air tight line in the whole house. Bar windows obviously!

Yes, this is a big advantage of having the dropped ceiling. Are you using uninsulated plasterboard below this?

ht9zni1gs28crp

BarneyMc wrote: »

Yes, this is a big advantage of having the dropped ceiling. Are you using uninsulated plasterboard below this?

Yes, all my critical insulation line is above the airtight line. Just means things can be moved or disturbed at later dates without the need to touch the fabric of the building. Also means Electrics and plumbing have all the space in the world to work with, without the need for me to follow on taping everything again and again.

BarneyMc

Bethany Breezy Jail wrote: »

Yes, all my critical insulation line is above the airtight line. Just means things can be moved or disturbed at later dates without the need to touch the fabric of the building. Also means Electrics and plumbing have all the space in the world to work with, without the need for me to follow on taping everything again and again.

But to get at these services again means tearing down plaster board or cutting the air tight membrane?

galwaytt

....its not just the ducting - having the unit itself on the warm side of the build is a factor too.

mfceiling

BarneyMc wrote: »

But to get at these services again means tearing down plaster board or cutting the air tight membrane?

Or like the lad whose house i worked on last year in Meath did...keep as many units/serviceable components etc in one room and install a "grid and tile" ceiling like you would see in an office or shop.

His reckoning was that he would probably be the only one who ever would be in that room, so aesthetics didn't really matter!!

BarneyMc

galwaytt wrote: »

....its not just the ducting - having the unit itself on the warm side of the build is a factor too.

Yes my unit will sit on the warm side. If the insulated ducting is sandwiched between the mineral wool in the attic then the heat loss will be negligent?

BarneyMc

mfceiling wrote: »

Or like the lad whose house i worked on last year in Meath did...keep as many units/serviceable components etc in one room and install a "grid and tile" ceiling like you would see in an office or shop.

His reckoning was that he would probably be the only one who ever would be in that room, so aesthetics didn't really matter!!

But you can only access a limited part of the ducting network here not to mention the other services?

893bet

BarneyMc wrote: »

Yes, this is a big advantage of having the dropped ceiling. Are you using uninsulated plasterboard below this?

Does the dropped cavity need ventilation?

mfceiling

BarneyMc wrote: »

But you can only access a limited part of the ducting network here not to mention the other services?

True - his room was about 4m x 3m. Full of services, main electric board, hrv unit, all computer equipment and his heat pump/boiler etc.

Rabbo

893bet wrote: »

Does the dropped cavity need ventilation?

No. Not if the insulation is above the service cavity

ht9zni1gs28crp

BarneyMc wrote: »

But to get at these services again means tearing down plaster board or cutting the air tight membrane?

No all services are forward or below the air tight line, yes access from the top would mean going through the insulation and air tight membrane. That decision can be taken if and when needed.

For now though I want to make my airtight membrane unbroken as much as possible.

ht9zni1gs28crp

mfceiling wrote: »

Or like the lad whose house i worked on last year in Meath did...keep as many units/serviceable components etc in one room and install a "grid and tile" ceiling like you would see in an office or shop.

His reckoning was that he would probably be the only one who ever would be in that room, so aesthetics didn't really matter!!

The way forward these days, I have a dedicated room or lift shaft as I call it that houses everything from MHRVC, Fusebox, Water tanks x 2, hot water storage, controls....This spans like a lift shaft up to ceiling height so all services have easy access to first floor and also ceiling void upstairs.

cerastes

Bethany Breezy Jail wrote: »

The way forward these days, I have a dedicated room or lift shaft as I call it that houses everything from MHRVC, Fusebox, Water tanks x 2, hot water storage, controls....This spans like a lift shaft up to ceiling height so all services have easy access to first floor and also ceiling void upstairs.

Am I reading that right? what type of building is this in?
It just doesnt seem to make sense to have a dedicated space with all services in it, ie water and electrics and everything else? assuming the worst and some kind of fault or leak? what then?
Aside from a seperate channel/space going up/down for electrical components/wiring and maybe MHR ducts could be smaller, than something that has incorporated a space for water storage and HW tanks and a MHRV unit? I ask because it seems unusual to me?

I had thought before that a dedicated channel up and down a house where a consumer unit is located (preferably hidden) would be a good way to make future electrical upgrades opposed to everything buried as seems to be the case and recently Id thought a good place to place heat recovery ducts.

ht9zni1gs28crp

cerastes wrote: »

Am I reading that right? what type of building is this in?.

Domestic

cerastes wrote: »

It just doesnt seem to make sense to have a dedicated space with all services in it, ie water and electrics and everything else? assuming the worst and some kind of fault or leak? what then?

The whole reason to have this area compounded and easily accessible.

cerastes wrote: »

Aside from a seperate channel/space going up/down for electrical components/wiring and maybe MHR ducts could be smaller, than something that has incorporated a space for water storage and HW tanks and a MHRV unit? I ask because it seems unusual to me? ?

Age old thinking calls this an Attic.....Which isn't easily accessible and again 90% of the time a total waste of footprint space...In my case of a story and a half there is little Attic space left when optimising space and volume

cerastes wrote: »

I had thought before that a dedicated channel up and down a house where a consumer unit is located (preferably hidden) would be a good way to make future electrical upgrades opposed to everything buried as seems to be the case and recently Id thought a good place to place heat recovery ducts.

This is what I have essentially described, except on a larger scale and houses all services required.

cerastes

Bethany Breezy Jail wrote: »

Domestic


The whole reason to have this area compounded and easily accessible.



Age old thinking calls this an Attic.....Which isn't easily accessible and again 90% of the time a total waste of footprint space...In my case of a story and a half there is little Attic space left when optimising space and volume

This is what I have essentially described, except on a larger scale and houses all services required.

I see, circumstances and needs. I thought the building might have been converted from some other use.
I would have thought its a very good idea except for having the water storage there too in the event (probably an outside chance) it creates a problem or worsens one. Id have thought having the water storage HW and CW in the same space also might make the space bigger than it would for electrical and ventilation alone. I thought there are regulations which state you cant have electrical services in a hotpress, I though the same might apply here.
Having said that, I can see the benefits for a channel up and down for services for a domestic situation, as it could make upgrades or changes done later easier, e.g. for adding lights or socket circuits or wiring for an electric shower if it were added later, opposed to services buried inaccessibly in the walls as they are now or where adding upgrades means doing damage or clipping something to the surface.

BarneyMc

miller_63 wrote: »

Dropped ceilings seems to be working well on paper for me so far....

I aim to keep everything inside the insulation line and so resulting in as few penetrations of the Air tight line as possible, I think I have three areas in total that penetrate my air tight line in the whole house. Bar windows obviously!

I was speaking to a fried about this at the weekend and his builder suggests creating a 2 inch service void in the bedroom ceilings. Would this really be enough for wires, water pipes, etc?

If this is not done then does that mean the wiring for every wall socket, light switch and light will penetrate the membrane?

Another inch and the (60mm) HRV ducting could be incorporated but I suppose it's yet another inch lost from the ceiling height.

ht9zni1gs28crp

BarneyMc wrote: »

I was speaking to a fried about this at the weekend and his builder suggests creating a 2 inch service void in the bedroom ceilings. Would this really be enough for wires, water pipes, etc?

If this is not done then does that mean the wiring for every wall socket, light switch and light will penetrate the membrane?

Another inch and the (60mm) HRV ducting could be incorporated but I suppose it's yet another inch lost from the ceiling height.

That was my view, by preventing multiple punctures of the membrane by careful predesign meant I could get everything into the voids...

BryanF

BarneyMc wrote: »

I was speaking to a fried about this at the weekend and his builder suggests creating a 2 inch service void in the bedroom ceilings. Would this really be enough for wires, water pipes, etc?

If this is not done then does that mean the wiring for every wall socket, light switch and light will penetrate the membrane?

Another inch and the (60mm) HRV ducting could be incorporated but I suppose it's yet another inch lost from the ceiling height.

The service cavity is the best option. this should have been decided before you broke ground

hexosan

BryanF wrote: »

The service cavity is the best option. this should have been decided before you broke ground

Bryanf I think we'd all love to live in your ideal world but unfortunately we don't.
I have had an architect & engineer engaged from the start of the build and if left only to their input id have a 100mm cavity with a few boards of insulation, walls dry lined (forget about plastered behind the boards) stick a few solar panels on the roof for that energy reg thing (part L) and drill a few vents in the wall cos that Airtightness thing will only cost you money.
Not all professional are as professional as you believe them to be. There are a vast majority ignorant to low energy or passive construction methods. Perhaps this could be kept in mind EVERY TIME engage/refer to a profession is suggested in posts where someone comes on here looking for advice.

BryanF

hexosan wrote: »

Bryanf I think we'd all love to live in your ideal world but unfortunately we don't.
I have had an architect & engineer engaged from the start of the build and if left only to their input id have a 100mm cavity with a few boards of insulation, walls dry lined (forget about plastered behind the boards) stick a few solar panels on the roof for that energy reg thing (part L) and drill a few vents in the wall cos that Airtightness thing will only cost you money.
Not all professional are as professional and you believe them to be. There are a vast majority ignorant to low energy or passive construction methods. Perhaps this could be kept in mind EVERY TIME engage/refer to a profession is suggested in posts where someone comes on here looking for advice.

There was a time when barney was going with the passive standard, what happened barney?

BarneyMc

BryanF wrote: »

There was a time when barney was going with the passive standard, what happened barney?

No, not me sir.

893bet

hexosan wrote: »

Bryanf I think we'd all love to live in your ideal world but unfortunately we don't.
I have had an architect & engineer engaged from the start of the build and if left only to their input id have a 100mm cavity with a few boards of insulation, walls dry lined (forget about plastered behind the boards) stick a few solar panels on the roof for that energy reg thing (part L) and drill a few vents in the wall cos that Airtightness thing will only cost you money.
Not all professional are as professional as you believe them to be. There are a vast majority ignorant to low energy or passive construction methods. Perhaps this could be kept in mind EVERY TIME engage/refer to a profession is suggested in posts where someone comes on here looking for advice.

Looks like we have the same architect and engineer.

ht9zni1gs28crp

That's crap to hear hexosan and 893bet in this day and age. I guess somethimes a lack of enthusiasm can hinder input.
A simple bit of legwork and foresight prior to final design sorts all these out. My Passive Certification is coming on a treat and im putting it all down to early design and detailing....

hexosan

Bethany Breezy Jail wrote: »

That's crap to hear hexosan and 893bet in this day and age. I guess somethimes a lack of enthusiasm can hinder input.
A simple bit of legwork and foresight prior to final design sorts all these out. My Passive Certification is coming on a treat and im putting it all down to early design and detailing....

My house was designed and planning got when I discovered low energy/passive building methods. At no point in the design process was it even mentioned to me. A lot of the knowledge gained and used came from the Internet and this site.
That's why it can get annoying when a question is asked here and all the poster gets is refer to you professional. Some on here have "professionals" who can't give an answer. I do agree that others come on here looking for free advise that they simply don't want to pay for.

ht9zni1gs28crp

Agree, this is where the likes of NZEB will step in, in the future this will grow and grow I guess especially its open doors format. Some people are happy to point people in right directions to help with decisions. I cant shut up about it, lol

rampantbunny

893bet wrote: »

Looks like we have the same architect and engineer.

...and me...we could have got a package deal.

Andrew_Doran

BarneyMc wrote: »

Ignoring the penetration of the air-tightness membrane, does it really make much of a difference having it here compared with having it in a service area below the joists?

For a 80m2 two story, with 1st floor served by ducts covered in 300mm mineral wool I think I worked it out at around a 1% overall loss in efficiency. Adding more insulation wasn't worth it (diminishing returns). Good workmanship and not over-sizing the ducts is more important (more duct surface area = more heat loss). Ductwork is one thing but unless you have no other good options putting the HRV unit itself in the attic is nuts.

http://www.wbdg.org/design/midg_design_tdcad.php

BarneyMc

Andrew_Doran wrote: »

For a 80m2 two story, with 1st floor served by ducts covered in 300mm mineral wool I think I worked it out at around a 1% overall loss in efficiency. Adding more insulation wasn't worth it (diminishing returns). Good workmanship and not over-sizing the ducts is more important (more duct surface area = more heat loss). Ductwork is one thing but unless you have no other good options putting the HRV unit itself in the attic is nuts.

http://www.wbdg.org/design/midg_design_tdcad.php

Thanks very much Andrew for sharing this. Interesting you mention the duct sizing. I was always aware that for ease of air flow a bigger duct is better but never thought about the conflicting fact that for heat loss it makes sense that a narrower duct is better. :rolleyes:

Rabbo

BarneyMc wrote: »

Thanks very much Andrew for sharing this. Interesting you mention the duct sizing. I was always aware that for ease of air flow a bigger duct is better but never thought about the conflicting fact that for heat loss it makes sense that a narrower duct is better. :rolleyes:

I would have thought the loss in efficiency due to friction in a narrow duct would be more of a factor than heat loss in a larger one. It's also worth bearing in mind that a narrower duct will be noisier

BarneyMc

Rabbo wrote: »

I would have thought the loss in efficiency due to friction in a narrow duct would be more of a factor than heat loss in a larger one. It's also worth bearing in mind that a narrower duct will be noisier

Yes indeed, there is always a trade off. I think a wide duct tucked under a warm blanket is the way to go!

Charlie Charolais

Is there any preference for solid or flexible ducting re MHRV ?

Calahonda52

Charlie Charolais wrote: »

Is there any preference for solid or flexible ducting re MHRV ?

Ther is some good quality flexible ducting which is smooth on inside and will bend 180 without kinking.
The downside is two fold, 1: limited to 32 cubic metres flow at 2.5m/s at I think 150 pascals pressure at the unit.
2: cost, but is easy to install.
The other issue is that diameter wise there is not a lot of choice

BarneyMc

BarneyMc wrote: »

I was speaking to a friend about this at the weekend and his builder suggests creating a 2 inch service void in the bedroom ceilings. Would this really be enough for wires, water pipes, etc?

If this is not done then does that mean the wiring for every wall socket, light switch and light will penetrate the membrane?

Went around to see this recently and am not sure now whether this IS the way to go. For one thing there is certainly a significant cost - material (lot of timber used) and labour. Also, it will mean the electrician having to drill through the batons (extra work).

Can I just ask, will there be a penetration for every light, light switch, electrical socket, HRV point in the airtight membrane? I suppose this all adds up but surely the membrane can be taped where these penetrations occur?

ht9zni1gs28crp

Hang the ceiling AFTER the first fix for all services. A few timber runners isn't going to break the bank as opposed to a couple of airtests to find leaks is!

If all your services penetrate the Air Tight line then Yes you have to deal with them accordingly.

rampantbunny

Is it not possible for those that are insulating at joist level, to just 'lift' the insulation and airtight membrane above the joists entirely, and then have their services underneath in the space between the joists. No penetration of the membrane.

You lose height in the attic but does it matter if the attic is essentially cold and unused.

[Edit]
On reflection, the airtight membrane would be under the joists and taped/stuck directly to the blockwork normally.
If you raised the membrane above the joists you have a lot of work to do bringing it down through the joists to the wall...but is it the lesser of two evils.

ht9zni1gs28crp

I think the original idea is that the services are all inbound of the membrane. By using the U/S of joist as Airtight line you are ensuring the best fit possible for air tightness because no penetrations and NO attempting to seal a membrane in and around joists.

rampantbunny

miller_63 wrote: »

I think the original idea is that the services are all inbound of the membrane. By using the U/S of joist as Airtight line you are ensuring the best fit possible for air tightness because no penetrations and NO attempting to seal a membrane in and around joists.

Comes down to what you're prepared to lose in ceiling heights versus the expense of extra labor and taping around joists I suppose.

Taping around joists must work though. Not aware of any other way of getting airtightness continuity if taking the airtight line from first floor walls up along the rafters (this is my case i.e. whole attic is inside the airtightness envelope).

BarneyMc

rampantbunny wrote: »

Comes down to what you're prepared to lose in ceiling heights versus the expense of extra labor and taping around joists I suppose.

Taping around joists must work though. Not aware of any other way of getting airtightness continuity if taking the airtight line from first floor walls up along the rafters (this is my case i.e. whole attic is inside the airtightness envelope).

My airtight membrane will be fixed to the underside of the joists and come down the walls and then taped, i.e. my attic is outside the airtight zone.

I've generous enough height on the 1st floor so could afford to go the batons route (service void). Would like to hear what folks are doing with theirs.

gooseygander

BarneyMc wrote: »

My airtight membrane will be fixed to the underside of the joists and come down the walls and then taped, i.e. my attic is outside the airtight zone.

I've generous enough height on the 1st floor so could afford to go the batons route (service void). Would like to hear what folks are doing with theirs.

My airtight membrane exactly as above taped to block walls on underside of joists. Duct runs and mhrv unit in cold attic, runs are all covered with soft touch insulation and all penetrations of airtight membrane resealed. Not sure if this is very best option but Suits me.

893bet

What are people using to attach the membrane to the joists? What I mean is my supplier has supplied a double sided tape that you run along the joists. Is this enough to hold it in place for a week or two while you get the blower test done and repair anything required? Or is counter banton required?

BarneyMc

gooseygander wrote: »

My airtight membrane exactly as above taped to block walls on underside of joists. Duct runs and mhrv unit in cold attic, runs are all covered with soft touch insulation and all penetrations of airtight membrane resealed. Not sure if this is very best option but Suits me.

So no service void under joists?

gooseygander

BarneyMc wrote: »

So no service void under joists?

Nope, only electric wires and mhrv ducts coming from attic, no water coming from attic. I would not have had the room height anyway for such a void. Ground to floor height currently is 8ft1in. To be honest even if I had the height I don't think I would have installed void.

rampantbunny

BarneyMc wrote: »

I've generous enough height on the 1st floor so could afford to go the batons route (service void). Would like to hear what folks are doing with theirs.

I'm jealous of all those with generous ceiling heights. Every house granted planning within a 5 mile radius of mine has had a restriction on height imposed as a condition.
When you view section details of the houses it looks near impossible to install an MHRV duct more than 75mm and maintain an 8ft'ish ceiling height on the ground floor.
It gets even tougher if you want to increase your rafter depths to get more insulation in between, or counter-batten the roof as it all pushes the height of the house up.

Anyway, I digress...back on topic. Barney, if I were you I'd put in the service void. Don't think I'd notice high ceilings in bedrooms as they are not exactly open plan...plus a lower ceiling probably increases the 'cosy' factor. Less holes to tape up in the membrane the better even if the tapes are top notch.

galwaytt

...isn't this alone a good reason to change to Open Web joists ??

hexosan

galwaytt wrote: »

...isn't this alone a good reason to change to Open Web joists ??

How do these compare in price to a length of 9x2