Jump to content

Recommended Posts

If you are trying to save money in the long run by making your house by insulating it good and making it as airtight as you can get it then you have to provide some method of ventilation, the easiest being mhrv. You can get complete systems for £2k which can be self installed fairly easy.

If you are going down the route of building regs type house with trickle vents in the windows then it would be a waste. 

The choice is up to you. 

Link to comment
Share on other sites

It;s not as easy as that I fear Have a read of this as a starting point to understand what is required - http://www.nhbc.co.uk/ProductsandServices/ConsultancyandTesting/Airleakageservices/documents/filedownload,38528,en.pdf

They mention that every new build requires an - Air Permeability Testing is a requirement for new buildings under Part L of the Building Regulations.

If a score of under 5 is achieved then an MVHR should be on your radar. Others will be able to explain more and in greater detail but the attached should get you up and running.

PW

Edited by Redoctober
typo
Link to comment
Share on other sites

No if you go down that route then when the time comes to spec your Windows and doors you can tell them no trickle vents or even a letter box. There is a lot more work involved getting a building airtight than just no trickle vents though.

 

Link to comment
Share on other sites

I believe MVHR is apart of a larger philosophy of 'materials first' as my architect likes to say. That is, put your money into the insulation and air-tightness of the structure to reduce your heating bills in the long term. Depending on the insulation you may also have significant performance in acoustic reduction. As an engineer I am quite fond of the philosophy as it focuses on simple and low maintenance technology rather than complex systems that would be higher maintenance and prone to breaking... I really don't like moving parts!

 

An MVHR not only provides ventilation but it is a good combo to further reduce your heating outlay whilst providing you with an improved environment (fresher air, filtered, quicker to dry towels/clothes etc...). For us it's a no brainier as all the above are #1 to #5 on our top 10 list of priorities. 

 

Out quotes have varied from £2k to £4k for the MVHR unit and the various ductings required too. Installation is often on top of this, but half of the suppliers wont even offer it. But as many will point out, installing a MVHR is a right of passage for many of the self builders on the forum!

  • Like 3
Link to comment
Share on other sites

Being the owner of a MBC passive standard house, I am happy to finally have a built in letter box in the new front wall vs a cardboard box that postie has used for the last 18 months, although I'll miss our chats.

 

A passive cat flap (£2k from memory) would also be welcome but aside from that I love the impact that air tightness & MVHR has on our house. When we had the recent -10 outside temps, we still could have the front door open for 20 mins with no draught or drop in temp.

 

 

  • Like 1
Link to comment
Share on other sites

15 minutes ago, Luckylad said:

Mvhr seems an excellent system. What size are the pipes? Does it matter if the unit is in the uninsulated part of my attic?

 

Pipe size depends on you requirements, If you install manifold system (most people do) then there are the pipes from the manifold which has many options depending on the system you use, the pipes from the MVHR unit to the manifold and the outside world, size depend on you overall system sizing.

If you put the unit in an un-insulated area then  it need to be insulated, and so do all the pipes (ducts) in the un-insulated area, you also need access to the unit for filter cleaning, so the best advice is in an insulated and accessible area.  Ideally it need to be considered form the outset of the house design as a retrofit will always have compromises.

Link to comment
Share on other sites

3 hours ago, Luckylad said:

Mvhr seems an excellent system. What size are the pipes? Does it matter if the unit is in the uninsulated part of my attic?

 

As @le-cerveau mentions, the size of ducting depends on the flowrate you need for each room.

 

There are minimum requirements for these per room/type as laid out in the Building Regs Part F (ventilation). These are laid out on page 19 (Table 5.1a/b) and there are some good examples on pages 51 (#C4) and 54 (#C8)

 

You can see on Ubbink's product page that there are several profiles (circular & ovular), each with various sizes to accommodate to the available space or flowrate requirements. These are an example of semi-rigid ducts which are ideal for a radial setup, but there are also rigid ducts that are better suited to a trunk and branch setup. Each system has it's pro's and con's as you can imagine.

 

The major factor in our selection of a MVHR supplier isn't just the unit, but the entire ducting system that goes with it and how friendly it is to DIY install. Even the design of such a system (i.e. the placement of the extract and supply valves, lengths of runs, flowrates etc...) can potentially be done as DIY too, but these services are available of course.

Edited by Visti
spelling
Link to comment
Share on other sites

We installed our first MVHR unit 15 years ago, in a then just to BR house.  The difference in internal air quality and no condensation vs the previous non MVHR house we had built (and every rental I've been in since) was huge.  For us, MVHR is worth every penny on that benefit alone.  Savings from heat recovery is just a bonus. I wouldn't consider building a house without MVHR.

Link to comment
Share on other sites

2 hours ago, Luckylad said:

Thank you both for the info and advice. 

I can put the unit in a cupboard in an office but the pipes will go through a cold roof area.

As usual I've got a lot of reading to do!

I have pipes that go through a cold area in my loft and all I did was sandwich them between some loft insulation. They sit on 200mm with another 200mm on top. 

Link to comment
Share on other sites

3 hours ago, Luckylad said:

Thank you both for the info and advice. 

I can put the unit in a cupboard in an office but the pipes will go through a cold roof area.

As usual I've got a lot of reading to do!

This is why it's good to discuss this before you are at the point of no return.

 

You have a room in your roof, so most of it will already be insulated at rafter level.  So insulate the entire roof at rafter level. It makes it easier to detail, to join the roof insulation to the wall insulation, and gives you 2 warm eaves spaces for storage or services.

  • Like 1
Link to comment
Share on other sites

1 hour ago, ProDave said:

This is why it's good to discuss this before you are at the point of no return.

 

You have a room in your roof, so most of it will already be insulated at rafter level.  So insulate the entire roof at rafter level. It makes it easier to detail, to join the roof insulation to the wall insulation, and gives you 2 warm eaves spaces for storage or services.

 

I agree, I have a warm roof ( usable loft space) so don’t have to worry about cable penetrations at ceiling level and insulation in the cavity is easy to join with rafter insulation.

Link to comment
Share on other sites

our insulation runs between and on top of rafters in the living space ,down the ashlar walls then across the ceiling to the cavity. We did this because we'd only fill up the attic space with stuff we'll never use. We've got a large storage cupboard on the landing. Im not keen on warm roof space because it seems a waste of energy to me, I also think the same of vaulted ceilings.

Link to comment
Share on other sites

Just now, Luckylad said:

I also think the same of vaulted ceilings.

 

We've gone with vaulted ceilings exactly because we don't want an attic to store stuff that'll never get used. Also, I'm of the taller pursuasion so I can't wait to have some decent headroom!

 

I think that's what great about self-builds; you get what you want! But boy are there a lot of decisions to clarify what that is...

Edited by Visti
Link to comment
Share on other sites

We've kept the vaulted ceiling that came with the design of our house because it looks nice but I do wonder about their impact on the environment . 99% of the properties I work on now have vaulted ceilings so it's adding up to quite a lot of volume that a few years ago would have been flat and unseated above.

So many decisions!!

Link to comment
Share on other sites

I don't see how  vaulted ceiling is "bad" fr the environment.

 

Yes is increases the heated volume.

 

BUT it is a LOT easier to get the detail right and maintain continuous air tightness and avoid services penetrating the insulation layer. So I suspect in practice a house with a warm roof vaulted ceiling will be a lot more eficcient than a cold roof loft with lots of leaks in the insulation layer.

 

Ours is room in roof, which is pretty much the standard for housing in the countryside up here, so part of it is habitable space anyway. It just made so much more sense to enclose the whole lot, loft storage space as well, inside the insulated envelope.

Link to comment
Share on other sites

If vaulted ceilings and warm loft  space increase the heated volume doesn't that increase the use of energy that otherwise wouldn't be used ?

I agree there's increased risk of leakage whenever surfaces go through insulation.

There's usually a draught when I work around downlights. 

I've only insulated my habitable space, if I'd insulated my cold roof area as well it would have doubled the heated volume in upstairs of my chalet bungalow.

 

Link to comment
Share on other sites

9 minutes ago, Luckylad said:

If vaulted ceilings and warm loft  space increase the heated volume doesn't that increase the use of energy that otherwise wouldn't be used ?

I agree there's increased risk of leakage whenever surfaces go through insulation.

There's usually a draught when I work around downlights. 

I've only insulated my habitable space, if I'd insulated my cold roof area as well it would have doubled the heated volume in upstairs of my chalet bungalow.

 

 

 

No, as in practice you will turn the ventilation rate down to suit the number of occupants, so it makes no difference how big the house volume is.  Ignore the building regs minimum for MVHR, as pretty much everyone finds that setting the MVHR to that figure over-ventilates the house (we run at around 2/3rds the building regs minimum and I think we're still over-ventilating a bit - we can probably reduce the ventilation rate by around 15% and still have better ventilation than a  house without MVHR.

Edited by JSHarris
Link to comment
Share on other sites

25 minutes ago, Luckylad said:

I agree there's increased risk of leakage whenever surfaces go through insulation.

There's usually a draught when I work around downlights. 

I've only insulated my habitable space, if I'd insulated my cold roof area as well it would have doubled the heated volume in upstairs of my chalet bungalow.

 

Downlights in a conventional house have bugged me for years. Not only were they a terribly energy hungry form of lighting (not so bad now with LED lamps) but they put a bloody great hole in the air tight and insulation layers when used upstairs in 99% of houses.  I used to hate them, and lost count of how many times I have removed a perfectly good 58W flourescent and replaced it with 300W or often more of halogen downlights.

 

Likewise switches and sockets. In most of the housing stock I work in, on a windy day when you remove a switch or a socket, a cold howling gale comes out of the hole.

 

In a well insulated house that has had some attention to air tightness in it's construction, and a warm vaulted roof, you will have NONE of those problems.  A good test of an air tight home is on a windy day, open one door or one window, and you won't feel a draught and it won't blow shut (or further open)

 

Insulating your entire roof space including the eaves spaces would  use less insulation (less surface area than insulating down the ashlar walls and across the ceiling) so cost less, and would be much easier to detail correctly, and you would not have to take any special measures to seal cables, pipes, ducts etc that pass through the eaves space. In your case if you stick to your plan, you are going to have a particular problem with any switches or sockets on your ashlar walls.

 

So much of the improvements we can make to buildings is not just about extra insulation, it's about attention to details to prevent massive air leaks. One such being create an air tight structure, then a service void within that before the plasterboard, so all cables and pipes have a free run without penetrating the building structure or it's air tight layer.

Link to comment
Share on other sites

 

17 hours ago, JSHarris said:

 

 

No, as in practice you will turn the ventilation rate down to suit the number of occupants, so it makes no difference how big the house volume is.  Ignore the building regs minimum for MVHR, as pretty much everyone finds that setting the MVHR to that figure over-ventilates the house (we run at around 2/3rds the building regs minimum and I think we're still over-ventilating a bit - we can probably reduce the ventilation rate by around 15% and still have better ventilation than a  house without MVHR.

Sorry I've probably made the comment in the wrong section, but I was referring to boilers heating up space that is not really used .

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...