Moisture Control, Supply of Fresh Air, Removal of VOCs.

The Past

Having lived in an house that had single glazing and was draughty, I only realised how inefficient the ventilation was when I purchased a Carbon Dioxide meter (CO2) for the old house. This meter measures the amount of carbon dioxide in a room (as we all exhale CO2). The bottom line is that a level below 1000ppm (part per million) is taken as a healthy starting point. Another factor that is not healthy is Volatile Organic Compounds (VOCs) these are the chemicals, gases given off by furniture, paints, floor coverings, household cleaning agents etc. When one reads the possible health effects from VOCs it becomes clear that one needs to reduce these. See for example

In our last home what was amazing was how little oxygen we were getting especially when asleep (and in turn high VOCs). Within an half an hour the meter would alarm that the levels of oxygen (fresh air) were low.

What I used to do in the old house is determine if there was a wind blowing or a storm due. This then entailed adjusting the window opening to a minimum in order to ensure that we would get some level of oxygen. If there was no wind blowing outside then I would open the window  to approximately 75 mm (The horizontal window was over a meter and a half long) and leave the bedroom door open for some cross ventilation through the house.

I think it is now widely accepted that holes in the wall or opening windows does not work for fresh air and a healthy environment. The only way that appears to work is to blow fresh air in / suck stale air out.

CO2 Meters

CO2 meters for some reason are expensive. The unit I purchased was over €300 a few years ago. I came across a more affordable unit recently on ebay for approximately €100 (allow for customs and excise) that also has a data logger (records the information over time). I feel it is well worth investing in one of these as the true quality of air in a house can only be believed when the CO2 levels are measured.

One seller on ebay was perfectprimetechnology . If one types in the word co2 at their store it should be easy to find or in any other store. 

CO2 Meter
Carbon Dioxide CO2 Meter

While there is no direct link between VOCs and CO2 I have read that if one is breathing air in a room with high CO2 levels it gives  a good indication that the VOC levels are also high.

Going Forward

In the new house we plan to use controlled ventilation which will supply fresh air and in turn recover some of the heat blown out of the house .  It is a mechanical system called a Heat Recovery Ventilation Unit (HRV). I do not know why they don’t call it a fresh air unit as this factor has to be more important than recovering heat. In order for this fresh air supply system to work one has to control all drafts in the house as one does not want to be drawing air in around windows and doors and hope that the fresh air ends up in the correct room. This can only be achieved by eliminating drafts by sealing the building in an air tight membrane/system and blowing fresh air in and extracting stale air out using two ducts.

In order to carry out airtightness in a home one appears to have a few options -On a block house this is achieved by internal plastering (and some preparatory work) or for a wooden frame house one can use a membrane or take a chance on using OSB (Oriented Strand Board). Even a block house will still need air tight membranes on some structural details.

Another reason for using this special air tight system is to control moisture generated in the house from showers, cooking, drying clothes etc. This moisture can have a detrimental effect on the building fabric and reduce the insulation levels and in a worse case scenario lead to mould growth.  I feel the mould issue is going to be a health issue for generations to come where insulation is added ad hoc to dwellings without a proper design using building physics. I am not aware of any building physicists in Ireland guiding the construction industry. A worrying trend I am hearing of is cases where the consumer believed that adding insulation was a good thing not expecting the creation of mould and health issues for themselves.

The Airtight Target for a Passive house

In order to control the ventilation and heat loss the passive house standard requires less than 0.6 air changes per hour at their test pressure. The best analogy I could find for this figure was at the web site. One must achieve no holes or less than one 18 mm hole for every 5 m2 of the building envelope. 

Passive Haus
Airtight Standard Passive House

Practical Experience of the first steps in airtightness

As I was installing counter battens on the ceiling in front of the airtight membrane I know from experience I missed the rafters in 3 locations in the roof. I am using serrated nails with a nail air gun. Once these nails are fired they are almost impossible to remove.

Serrated Nails

The strategy is not to try and remove them as this would leave a hole other than a nail in a hole behind the batten.

Battens on Ceiling

Installing battens on the ceiling

Another factor is to ensure that the insulation does not sag below the rafters before the airtight membrane is installed.

When one is laying out the membrane one needs to work in a triangle when stapling. For example staple 3 metres  or more forward on one side and then find the centre of the other side and staple from this point to either side.  Ensure that stainless steel staples are used as there is very little in the price difference.

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