Airtight house ventilation

[bragan]

Hi All,

My partner and I are in the process of building an air tight, timber frame house. Our house will be ventilated using airvents in the windows.

Has anyone built an airtight house and used window vents for ventilation. My concern is that this will not provide enough ventilation, and our house will be damp/smelly/mouldy or cold in the winter because we have to open the air vents.

I have heard about the mechanical ventilation units recently, but our building contractor never mentioned this to us, and seems to think the window ventilation will be enough.

 

[onq]

Hi All,

My partner and I are in the process of building an air tight, timber frame house. Our house will be ventilated using airvents in the windows.

Has anyone built an airtight house and used window vents for ventilation. My concern is that this will not provide enough ventilation, and our house will be damp/smelly/mouldy or cold in the winter because we have to open the air vents.

I have heard about the mechanical ventilation units recently, but our building contractor never mentioned this to us, and seems to think the window ventilation will be enough.

------------------

Hi Bragan

I am not certain your builder is the person who should advise you on this matter.
I am not clear on what you mean by airvents in windows.
There are other things to consider:

Part B of the building regulations is here:
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1640,en.pdf

1st Floor windows provide secondary means of escape in event of fire.
Section 1.5.6 refers

You can emply other means to reduce the dependency on jumping out of first floor windows:

• increase compartmentation
• upspec the FD& A system
• put a window-shattering awl in each room

But let's face it, if you have the option its easier to install a compliant opening window.

Part F of the building regulations is here:
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1647,en.pdf

Background ventilation is requried for habitable rooms of 6500sq.mm.
(that's millimetres not metres).
Rapid ventilation to 1/20 the floor area is also required.

Many "sealed" houses have MVHR systems included in their specification.
This is an "improvement" mentioned by the DEAP appendix Q.
These don't work well with permanent 6500 sq.mm. vents.

If you seal the house totally you don't comply with Part F.
If you turn off the MVHR system you have no ventilation.
If the power fails you may have no ventilation or heat.

Think outside the box: use multiple redundant systems.

FWIW

ONQ.

 

[who, me?]

Well kitchens and bathrooms require seperate mechanical ventilation for a start. It can be possible to ventilate using window vents however its not by any means the best way! The issue is one of control.
With any means of natural ventilation the benfits of an air-tight house are reduced. 90% of airtight houses use heat recovery ventilation (HRV)

My advice is scrap the window ventilators and install a HRV system. They are relatively cheap (around 2000-3000). They give so much more control and comfort, i can almost gauruntee you wont regret it.
Also theyre quiet easy to retrofit so dont feel as if the build has gone to far, its probably not too late

 

[threebedsemi]

bragan,
you should also look into 'passive stack ventilation' systems. these are available from richmond and also a company in cork called aereco. i haven't used these systems myself as yet, but they would seem to get around the hole-in-the-wall/windowframe problem if you dont want to go down the mechanical route.

 

[onq]

bragan,
you should also look into 'passive stack ventilation' systems. these are available from richmond and also a company in cork called aereco. i haven't used these systems myself as yet, but they would seem to get around the hole-in-the-wall/windowframe problem if you dont want to go down the mechanical route.

I'd be inclined to think you're correct - however...

PSV's are listed as options for Kitchens, Utility Rooms and Bathrooms only, not habitable rooms.

This is the problem.

Plus, if you rely totally on a MVHR system, where are you when the power cut occurs - with no ventilation.

And you cannot turn it off, ever.

Nope, there has to be a better way and I think Part F is beign re-written to take account of hybrid stack-and-mechvent systems as discussed at the Plan Expo 2009 conference.

Mind you, even with these state-of-the-art systems, you may need to change the filters every three months and ideally every month.

Can you see Joe Soap doing this even once a year? I can't.

That's heading for sick building syndrome territory.

That's one reason that perma-vents were in the regs originally.

And now we've so many people jumping on the Part L bandwagon without thinking.

It'll all end in blocked vent filters, toxic mould, tears, wheezing and asthma, wait and see.

What eejit decided we absolutely need 20 degrees of heat all year round in the house anyway>?

We need to become Georgians - go horse riding, eat well, wear three layers of clothing and take a cold bath once a month.

If you think its necessary!

ONQ.

 

[bragan]

Thanks everyone.

Firstly, we do have fire escape windows on the first floor. Secondly, we will have mechanical ventilation in the kitchens and bathrooms, but as that is standard in every house regradless of whether it is airtight or not, i didn't think that would be enough.

As we are already too far along to put vents in our walls, i'll look into the other options mentioned. Thanks!

 

[RKQ]

we will have mechanical ventilation in the kitchens and bathrooms, but as that is standard in every house regradless of whether it is airtight or not, i didn't think that would be enough.

MVHR is mechanical ventilation. It is based on the idea of removing moist warm air from bathrooms & kitchens, expelling this warm air externally but using it to heat the cold air being taken in from the outside.

MVHR systems can have "washable" filters. But as ONQ says its very important to clean & maintain these filters. Which is not always easy or convenient in our busy lives.

Its also worth noting that may people blocked up or removed there chimneys in the UK, when Gas heating was cheap and common. Then people started to notice the huge increase in Asthma and the lack of natural ventilation was the cause.

Maybe Airtightness is the wrong phrase - maybe we should call it "controlled air movement".

 

[onq]

<snip>
As we are already too far along to put vents in our walls, i'll look into the other options mentioned. Thanks!

You're never too far along to put a hole in a wall.



Personally, and although I remain to be persuaded fully, the combined system (passive stack with mechanical ventilation) seems a good compromise.

Part B of the regulations is here (again)

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1640,en.pdf

As Duncan Stewart reminds us "carbon monoxide is a silent killer".

1. There remain huge issues with sealing and cross-ventilation from vent to vent should a fire start at ground floor level where it initially produces cold smoke and fumes, especially where there is a sleeping occupancy upstairs.

2. Whatever venting system becomes used in practice will also have to address fire penetration issues.

The 1st floor is supposed to offer 1/2 hour fire resistance (FR30) and holes in the ceiling below from downlighters are bad enough - there are FR30 hoods to help combat this.

However internal ventilation ducts passing through the house from ground to attic pose a significant risk of fire spread to all levels - these may require some form of collar at the open end and probably enclosure with FR30 construction for the entire length of the duct.

These issues of Building Regulation inter-operability do not appear to be addressed in the "Acceptable Details" on the DOE website. I would be more than happy if someone was in a position to contradict me, or who knows of a system is use somewhere which addresses the issues mentioned above and could post a link.

(some of the above will be copied to the FAQ I think)

ONQ.

 

[Sconhome]

There are intumescent collars and seals that are used with pipe penetrations to maintain the fire rating and integrity of the fire stopping.

 

[onq]

There are intumescent collars and seals that are used with pipe penetrations to maintain the fire rating and integrity of the fire stopping.

<nods>

Hi Sconhome,
Boring, miserable, wet Sunday isn't it?

Well here goes another draft for a section of the FAQ.
BTW, I hit the 40,000 character limit for a single post last evening.
Dividing the Self Build FAQ into separate posts 1, 2, 3 etc. is my next task.
Moving right along...

I'm not certain all the types of collars or fire rope will work as intended in a domestic ceiling context, but some versions may.
The substrates the fire collars seal to tend to be much more robust than the single sheet of 12.5mm plasterboard in a domestic ceiling.

You normally specify collars and seals in commercial or institutional developments.
Thus they would be used in services penetrations in buildings where an active occupancy arises.
Otherwise they may be where active carers or managers can react to the initial fire alarm - a hotel, hospital or nursing home for example.

The sleeping occupancy of a house is not monitored and must first be protected and then awakened.
Long before heat from the fire has activated the smoke collar the occupants could die from CO or fume inhalation.
Its one of the reasons its so important to prevent interstitial spaces running continuously behind dry lining and into the floor void above the ground floor ceiling.

Its also one of the weaknesses of protection offered by FR30 hoods on downlighters unless they are well-sealed with paste and not just pinned.
Which in turn is another reason to use low voltage light fittings - less voltage in general implies less power to be used = less heat generated.

Mind you, in two of the fire scenes I have inspected it was a transformer that caused the fire risk, not the fittings.
One answer is to specify transformers which shut themselves off when there is a heat build up or short.

All of which attempts to comply with Part B will tend push up the price for MVHR/hybrid systems.
But achieving reductions in energy usage without taking steps to avoid increasing fire risk could be unwise at best and criminal at worst.

This partly why at Plan Expo 2009 I called on to the Government put some of those six figure civil servants to work producing a set of working drawings for a simple dwelling showing how to address all Building Regulations compliance issues in an integrated holistic manner, not just Insulation and Sealing.

The Government needs to stop simply raising the bar on Conservation of Fuel and Energy [Part L] in an isolated, simplistic fashion.
The DOEHLG needs to help establish deemed-to-comply standards for achieving Carbon Neutral Dwellings by 2013 or it simply won't happen.

FWIW

ONQ.