Alternative to trickle vents?

[Adamantium]

Hi all,

 

I'm currently speccing (before build) a neo georgian house and have decided on bygone windows. The issue is that for authenticity reasons they do not have trickle vents - fantastic. My concern is meeting the ventilation requirements for a new build home. I do not want to install ugly airbricks but what choice do I have?

 

Any advice would be much appreciated.

 

Adam

[Mr Punter]

MVHR.  Will really help with your SAP calcs too and far better air quality than trickle vents.

[Jeremy Harris]

Given the large areas of glazing, I think MVHR will be essential, just to get an acceptable energy performance to get through building regs.  It also improves the indoor air quality a fair bit, and that alone would be a good reason to fit it.. 

[Adamantium]

So it's not that trickle vents are required as such, it's more that the SAP calcs need to stack up.

 

Approximate cost of MVHR?

[Crofter]

It's not just a theoretical or regs-meeting thing: if you don't have some sort of ventilation, you'll end up with mould and condensation at best, and increased CO/CO2 levels at worst,

 

MVHR costs are obviously highly dependent on size of house and specification level. Just to give a data point, I spent about £750 on a fairly well equipped unit (auto bypass, control via humidity, timer, etc) albeit on a very small house. I think for average sized houses people spend in the region of £2k, so in the scheme of a large house build it needn't be an enormous cost.

[Jeremy Harris]

Bear in mind that to just meet building regs the house will have to be moderately air tight, considerably more airtight than a house built 15 or 20 years ago.  This means you need to plan for a means of ventilation, one that will be effective at combatting the potential problems that @Crofter has highlighted.  As you need good ventilation anyway, it makes sense to recover waste heat at the same time, both to reduce running costs and improve comfort.  I'd argue that the improved level of comfort from fitting MVHR is a good enough reason to fit it; it really does make a house feel a lot nicer indoors.

[ProDave]

A self builder here is in a predicament. He is building a pretty well insulated house and detailing the air tightness well. But he has chosen not to fit mvhr. Instead he has a central extract system on each floor extracting from the bathrooms, kitchen and utility and trickle vents on the windows.  After his air tightness test he was told it was "too good" and he is now looking at adding positive input ventilation as well (i.e mechanical ventilation without the heat recovery)  I did try telling him mvhr was the way.......

[Stones]

MVHR really is a must. We've lived with MVHR since 2003, and I wouldn't consider not installing it, because the improvement to internal air quality vs a house without is considerable. Heat recovery is a bonus.

[Ian]

@ProDave

+1 on that issue with the Building Regs.

On my own build I made an early decision to not have MVHR but it greatly complicates the situation with Building Regs and adds a lot of uncertainty.

The min allowable air tightness rate without MVHR is 3 m3/(m2.hr)@50Pa.

Luckily I achieved a figure of 3.7 m3/(m2.hr)@50Pa at my first air pressure test which was obviously a big relief but frankly it would have been less stressful to have made an early decision go with MVHR and to aim for a better air tightness figure.

[Stones]

@Ian Out of interest, what was your reason for deciding not to install MVHR?

[Ian]

33 minutes ago, Stones said:

@Ian Out of interest, what was your reason for deciding not to install MVHR?

@Stones

I wanted to keep things as simple as I could. 

The building is a small (71m2 nett) single storey holiday home 

[Crofter]

38 minutes ago, Ian said:

@Stones

I wanted to keep things as simple as I could. 

The building is a small (71m2 nett) single storey holiday home 

 

I'm 43m2 single storey. Still went with MVHR primarily because the site is quite exposed and in my existing house, just over the road, I am forever opening and closing trickle vents as the wind goes from zero to howling gale. You can't just leave them closed, because the windows run with condensation and the frames grow black mould. But you can't leave them open because of the noise and the heat loss.

 

By the way, I seriously considered using a single room unit instead- you might want to consider that as it would be a much less intrusive installation.

[Ian]

42 minutes ago, Crofter said:

By the way, I seriously considered using a single room unit instead- you might want to consider that as it would be a much less intrusive installation.

@Crofter

We completed our build 4 months ago. Everything seems to be working well and we're happy with the way it turned out.

It's a timber frame building from a local Welsh company clad with UK cedar.

Although the insulation levels only just exceed minimium overall Building regs standards and are not up to the levels of some of the fascinating builds I've read about on this forum the U values aren't bad:

0.1 concrete floor (with Hive controlled wet u/floor heating)

0.13 warm (cathedral) roof

0.21 walls (thin walls to maximise internal space)

0.8 windows (Rehau 3g)

 

As it's such a small building energy use is tiny.

 

We're now in the middle of sorting out the site: 1.5 acres of Welsh mountainside but we're hoping to have it all finished by the end of the summer.

Edited June 1, 2017 by Ian

[Crofter]

@Ian That is not shabby at all! Far better than the vast majority of houses, I would think.

I wonder sometimes if we get carried away with energy use per m2 rather than actual useage per dwelling- the PassivHaus system lends itself to making bigger houses. We don't consider our cars to be more economical if they use less diesel per tonne of car, do we?

[Ian]

@Crofter

we have no mains gas so I went for bulk LPG and a combi boiler. As I'm sure you know, SAP penalises you if you don't have mains gas so you end up with higher insulation values to compensate.

[Jeremy Harris]

Strictly speaking, SAP doesn't penalise any fuel, all it does is reasonably accurately reflect the environmental impact of all domestic fuels.  Mains gas is a pretty low emissions fuel, which is why using it usually gives a better rating, whereas oil and LPG are both significantly worse, because of the energy used to refine and transport the stuff, amongst other things.  We're all-electric, as there's no mains gas here.  Still managed to get an EPC of A107 though, and an EIR of 107, at -0.9 tonnes of CO₂ per year.

[designerC]

On 01/06/2017 at 19:39, Ian said:

@ProDave

+1 on that issue with the Building Regs.

On my own build I made an early decision to not have MVHR but it greatly complicates the situation with Building Regs and adds a lot of uncertainty.

The min allowable air tightness rate without MVHR is 3 m3/(m2.hr)@50Pa.

Luckily I achieved a figure of 3.7 m3/(m2.hr)@50Pa at my first air pressure test which was obviously a big relief but frankly it would have been less stressful to have made an early decision go with MVHR and to aim for a better air tightness figure.

Can I ask what system you did instead? ta

 

[Ian]

22 hours ago, designerC said:

Can I ask what system you did instead? ta

 

The old fashioned way- natural ventilation via windows that open. Also you’re supposed to have trickle vents on the windows.