Design/Fabric new build considerations for someone sensitive to dry indoor air

[thaldine]

Hello,

 

In all buildings I've so far lived in I have a problem with irritated nasal linings and congestion (not allergy related). Stepping outside relieves it rapidly and coming back indoors brings the symptoms back almost as quickly. Symptoms seem to be worse during windy and/or cold weather (especially when both windy and cold). I suspect the greater the propensity for moisture to evaporate within the home the worse the symptoms get. Based on that, what should I pay attention to in the design, bearing in mind the general guidance to avoid indoor condensation ?

 

The planned build has 0.6 ac/h air tightness and vapour control barrier.

 

Thanks,

Trish

 

Edited June 5 by thaldine

[JohnMo]

I would go UFH, which tends to radiate heat unlike radiators. However any heated house will lower the relative humidity. But a little fine tuning of ventilation rates should assist with that and maybe an enthalpy heat exchanger in the MVHR.

 

 

[ProDave]

In old houses I doubt too low humidity is your problem.  It would be good to identify what you are trying to avoid.  Start by getting a hygrometer in the house that affects you.

 

I think most people with an mvhr like me report good internal air quality as one of the benefits.  Have you ever been in a house with mvhr?

[thaldine]

@ProDave I've had a hygrometer for a few years and when the indoor RH undergoes a drop (equally say from 65 to 45 or 50 to 30) as it does when windy the symptoms are at their worst. I'm not sure it is to do with the outright value of the RH but more the fact it drops quickly (possibly leads to the propensity of moisture to condense on a surface to lessen ?) Similarly, when RH is high it can be a bit of an issue too but not as bad as during an aforementioned drop (I wonder if this is because a good proportion of any moisture has been locked up as vapour hence the high RH). No, I've never spent more than a couple of hours in a MVHR equipped house. So when you mention good internal air quality do you put that down to any specific characteristics ?

 

@JohnMo Thanks, I'd landed on the UFH and enthalpy exchanger so it's encouraging to hear it echoed that those may both be worthwhile in relation to the problem !

[JohnMo]

19 minutes ago, thaldine said:

@ProDave I've had a hygrometer for a few years and when the indoor RH undergoes a drop (equally say from 65 to 45 or 50 to 30) as it does when windy the symptoms are at their worst. I'm not sure it is to do with the outright value of the RH but more the fact it drops quickly (possibly leads to the propensity of moisture to condense on a surface to lessen ?) Similarly, when RH is high it can be a bit of an issue too but not as bad as during an aforementioned drop (I wonder if this is because a good proportion of any moisture has been locked up as vapour hence the high RH). No, I've never spent more than a couple of hours in a MVHR equipped house. So when you mention good internal air quality do you put that down to any specific characteristics ?

 

@JohnMo Thanks, I'd landed on the UFH and enthalpy exchanger so it's encouraging to hear it echoed that those may both be worthwhile in relation to the problem !

This is a couple of trends of house and summer house. The house is MVHR (but not enthalpy). The second is a heated summer house with dMEV. The trends run from January and you can see when the heating was switched off there is a jump in RH humidity. But it does show an almost flat line in the house. Reducing ventilation rates would fix this.  Something like Fresh-R ventilation will do this automatically as it does MVHR based on demand of humidity and CO2 sensed from the extract.

 

House - MVHR

 

Summer house with dMEV.

 

 

 

 

[ProDave]

50 minutes ago, thaldine said:

@ProDave I've had a hygrometer for a few years and when the indoor RH undergoes a drop (equally say from 65 to 45 or 50 to 30) as it does when windy the symptoms are at their worst. I'm not sure it is to do with the outright value of the RH but more the fact it drops quickly (possibly leads to the propensity of moisture to condense on a surface to lessen ?) Similarly, when RH is high it can be a bit of an issue too but not as bad as during an aforementioned drop (I wonder if this is because a good proportion of any moisture has been locked up as vapour hence the high RH). No, I've never spent more than a couple of hours in a MVHR equipped house. So when you mention good internal air quality do you put that down to any specific characteristics ?

Our house is well insulated, air tight and ventilated with an enthralpy mvhr unit.  The hygrometer barely moves currently sitting at 58%  I have never seen it above 60 or below 50 and it only ever changes very slowly.

 

That is no guarantee that it would help your condition but it sounds hopeful.

 

A house without mvhr has pretty much random ventilation, largely depending on how windy it is.  At times it will be unfer ventilated and stuffy, at other times over ventilated and cold.  Our new house is never too hot or cold, never draughty yet constantly has fresh feeling air inside.

[JohnMo]

4 minutes ago, ProDave said:

ventilated with an enthralpy mvhr unit. 

@ProDave @thaldine our house is sitting at 42% RH currently and its 21.5 degs, we have had a bedroom window open all day and lounge windows open this evening. But outside is 79% humidity and 7 degs.

 

5 minutes ago, ProDave said:

The hygrometer barely moves currently sitting at 58% 

It's interesting to see the difference between the enthalpy HE compared to stock heat exchanger.

[Kelvin]

58% seems quite high as it’s right at the top of the healthy range. Although the standard MVHR unit has the RH right at the bottom of the range. The difference is interesting. 
 

If I switch the MVHR off the RH goes up to the low to mid 50s and with it on it sits around 42%.  Temp is currently 21.5C
 

 

Edited June 6 by Kelvin

[Temp]

 

On 05/06/2024 at 14:33, thaldine said:

Stepping outside relieves it rapidly and coming back indoors brings the symptoms back almost as quickly

 

In cold weather/winter the air outside is frequently drier than indoors. So I'm thinking it might not be a low humidity problem. 

 

Could it be dust mites? We designed our house to have mostly tiled, stone and wood floors rather than carpets and that helped me quite a bit.

 

 

[Iceverge]

@thaldine

 

Move here to the West of Ireland where for 11 months of the year everything is DAMP DAMP DAMP!!!

 

Seriously though, I would advocate building a passive house. 

 

An ERV like this will maintain the humidity at your desired level without having to resort to under-ventilation to raise the RH Levels. (This will bring other issues like high VOCs and CO2)

 

 

 

The better you can make your airtighess the better too. Otherwise you'll still be at the mercy of the weather which seems to be making your symptoms worse. 

 

Thermal bridge free design should help keep any condensation spots from developing too. This is important because these moist corners are where moulds and insects like to breed. 

 

The lack of drafts and cold spots will make the house comfortable at a lower internal air temperature which will result in lower RH levels too.