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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorsuperfurry
    • CommentTimeOct 5th 2020 edited
     
    Hello all,

    First time poster long time reader. Please feel free to move this post if there is a better place for it. Appreciate your thoughts on this.

    We have been living in a late victorian house for 7 years and the kitchen is right at the back (house is very narrow and long). Looks like the kitchen has been drylined with stud walls at some stage.

    In April our boiler packed in during lockdown (bad timing also because my wife was pregnant and lots of expense for baby on the way too!). When the engineer came we realised the old boiler was hung in a shallow cut out recess on the solid wall behind the studwall. Presumably because that was the safest option with the weight of the boiler. i had never thought about it before.

    The new boiler hung on the same wall was a different size and piping configuration which has left us with two gaps above and below the boiler as you will see here with the before and after pics (click on link):

    https://photos.app.goo.gl/TQgo5pnjd2ZccGRJ9

    I can feel a slight draught coming from the gaps around boiler so presumably the space between the wall and stud wall isn't airtight - it is worse in windy weather which isn't very energy efficient. The previous boiler was not sealed in completely, there was a smaller gap underneath where the pipes came out from underneath into the boiler etc (see from pics above). But this is a much larger gap.

    Apart from the draughts it doesn't look very good so I am looking at having it made good/boxed in to be similar to before except the magnetic filter sits proud of the wall so can't put anything flush below the boiler.

    Ideally I would have it all completely sealed up tight with an access hatch for the servicing pipes. But i have read you should allow ventilation whenever gas pipes are behind a stud wall so you can smell a leak/gas can dissipate/doesn't build up in a void. So i expect i will have to leave some vents/gaps. I expect it will be impossible to get it airtight from the kitchen side anyway without moving the boiler and re-plastering the gap.

    I was wondering if anyone had any suggestions for tidying it up in a practical way. I am also wondering if i should be concerned about condensation in that space if it isn't completely sealed. I am thinking it might be OK as it was ventilated before from underneath and I can't see any damp/mould on the exposed solid wall that was previously covered up. The wall is also not a cold external wall (the downstairs toilet backs onto it) which would hopefully minimise possible condensation. We also try and keep water vapour to a minimum in the kitchen - opening windows, extractors and using a dehumidifier in the laundry area. RH usually stays around 45-55% peaks at dinnertime to about 60%-65% sometimes a little more but drops shortly afterwards. I am just a little paranoid about mould and look at any chance to minimise it occuring.

    Apologies for the lengthy post hope it is clear! Thanks in advance for any thoughts etc.
    • CommentAuthortony
    • CommentTimeOct 6th 2020
     
    Simplest would be an MDF or wood overlay frame round it. And a hinged or removable box under it, all painted as the wall and all could be removable or just the one over it

    I would wodge fibreglass tightly in any gaps that you can get at all round before

    I have a lot of problems with holes/gaps round pipes to outside so would seal from outside round any pipes that go through the wall and round the flue too

    There are people that can extend the plasterboard but I wouldnt do that too expensive and likely to be problematic / get damaged during servicing

    clean filter now then in a week then in a month then 3 months then annually
  1.  
    Posted By: superfurryI can feel a slight draught coming from the gaps around boiler so presumably the space between the wall and stud wall isn't airtight - it is worse in windy weather which isn't very energy efficient.

    That implies that the draught is coming from the outside rather than from convecting internal air. If it is from the outside then it sounds like you have a 'plasterboard tent' (one of Tony's descriptions of modern build) It isn't the space between the wall and the stud wall that isn't air tight but the wall itself that isn't air tight, letting in the cold - more so when windy..

    It really would be worth finding the source and fixing it because even if you seal up around the boiler the wind wash will go somewhere else and it will always cost energy (= money) and provide an easy source of mould production somewhere.
    • CommentAuthorsuperfurry
    • CommentTimeOct 6th 2020 edited
     
    Posted By: tonySimplest would be an MDF or wood overlay frame round it. And a hinged or removable box under it, all painted as the wall and all could be removable or just the one over it

    I would wodge fibreglass tightly in any gaps that you can get at all round before

    I have a lot of problems with holes/gaps round pipes to outside so would seal from outside round any pipes that go through the wall and round the flue too

    There are people that can extend the plasterboard but I wouldnt do that too expensive and likely to be problematic / get damaged during servicing

    clean filter now then in a week then in a month then 3 months then annually


    Thanks for the suggestion - when you say frame do you mean like a cupboard frame around the whole boiler? I was thinking of a box just at the bottom and some boarding at the top. I think the problem I have is that the boiler and the gas pipe need some kind of ventilation into the room so I can't make it completely airtight.
  2.  
    Posted By: Peter_in_Hungary
    Posted By: superfurryI can feel a slight draught coming from the gaps around boiler so presumably the space between the wall and stud wall isn't airtight - it is worse in windy weather which isn't very energy efficient.

    That implies that the draught is coming from the outside rather than from convecting internal air. If it is from the outside then it sounds like you have a 'plasterboard tent' (one of Tony's descriptions of modern build) It isn't the space between the wall and the stud wall that isn't air tight but the wall itself that isn't air tight, letting in the cold - more so when windy..

    It really would be worth finding the source and fixing it because even if you seal up around the boiler the wind wash will go somewhere else and it will always cost energy (= money) and provide an easy source of mould production somewhere.


    Thanks Peter that is interesting. I have never heard of wind tents before. Is this common in new build properties? I suspect it might be coming from the floorboards below or the roofspace (slanted roof with void, no access hatch) above but without demolishing plaster walls/ceiling and/or taking up the floor it is going to be really tricky and expensive to find out.

    When you say the wind wash would provide an easy source of mould production - I was wondering if a little fresh air from the outside would be better than a stuffy space receiving trickles of air from inside the house? i.e. like an airbrick venting effect. But that probably shows how little I know about these things.
  3.  
    Modern build houses often have plasterboard (PB) linings to the walls as this is cheaper than wet plastering. The PB is often fixed by dot and dab. (dollops of adhesive to the back of the PB which is then applied to the wall. The problem arises because there is a howling gale through the cavity and the inner skin is full of holes due to careless bricklaying. This allows the cold air to circulate behind the PB removing a good quantity of the heat regardless of the thermal properties of the wall. Tony uses the phrase PB tent to describe this problem as houses built with this have all the insulative properties of a plaster board tent.

    Occupied houses will have a high relative humidity (RH) just by people living. A high RH will cause condensation on a cold surface. If a wall is cold then condensation will form and where there is condensation mould will follow. So if If your PB stud wall has cold external air behind it then it will be at a lower temp than other places so this is where any condensation will occur and mould will appear. If you have a cupboard standing against this wall then behind the cupboard is where the mould will first arrive (due to reduced air flow at that point).

    The mantra - build it tight, ventilate right - works because you don't want uncontrolled air (= draughts) coming into your house, on the other hand you need sufficient controlled ventilation to keep the RH down to about 50% - 60% to avoid problems.

    In the old days when windows and doors leaked like sieves then uncontrolled ventilation happened there and via the open coal fire place (and not through the walls which were wet plastered) but there were different standards of heating and expectations. Come today with focus on energy use, air tight windows and doors and different expectations care has to be taken to avoid mould problems which is where MVHR (mechanical ventilation with heat reclaim) becomes necessary with a well built modern house.

    If you search through this forum you will find people spending considerable effort to make their place as air tight as possible as (usually) the best way to reduce energy consumption. After the place is substantially draught free then insulation makes sense.
  4.  
    Posted By: Peter_in_HungaryModern build houses often have plasterboard (PB) linings to the walls as this is cheaper than wet plastering. The PB is often fixed by dot and dab. (dollops of adhesive to the back of the PB which is then applied to the wall. The problem arises because there is a howling gale through the cavity and the inner skin is full of holes due to careless bricklaying. This allows the cold air to circulate behind the PB removing a good quantity of the heat regardless of the thermal properties of the wall. Tony uses the phrase PB tent to describe this problem as houses built with this have all the insulative properties of a plaster board tent.

    Occupied houses will have a high relative humidity (RH) just by people living. A high RH will cause condensation on a cold surface. If a wall is cold then condensation will form and where there is condensation mould will follow. So if If your PB stud wall has cold external air behind it then it will be at a lower temp than other places so this is where any condensation will occur and mould will appear. If you have a cupboard standing against this wall then behind the cupboard is where the mould will first arrive (due to reduced air flow at that point).

    The mantra - build it tight, ventilate right - works because you don't want uncontrolled air (= draughts) coming into your house, on the other hand you need sufficient controlled ventilation to keep the RH down to about 50% - 60% to avoid problems.

    In the old days when windows and doors leaked like sieves then uncontrolled ventilation happened there and via the open coal fire place (and not through the walls which were wet plastered) but there were different standards of heating and expectations. Come today with focus on energy use, air tight windows and doors and different expectations care has to be taken to avoid mould problems which is where MVHR (mechanical ventilation with heat reclaim) becomes necessary with a well built modern house.

    If you search through this forum you will find people spending considerable effort to make their place as air tight as possible as (usually) the best way to reduce energy consumption. After the place is substantially draught free then insulation makes sense.


    Peter you have been very generous with your knowledge here. Thanks. I see what you mean now. So the cold air could lower the surface temp of the stud wall insulation and create the 'cold wall' effect it was trying to prevent in the first place!

    I think we have been lucky as on this wall there is a dishwasher and cabinet under the sink and in the 7 years we have been here no mould growth on it so perhaps the surface temp isn't too bad. We are careful to ventilate the kitchen as well and keep the RH as low as possible with use of extractors etc. We have an issue in our old bedroom on a cold north facing external brick wall with furniture up against it so I am conscious of what you say re furniture up against colder walls.

    Seems like a delicate balance of ventilation vs draughts. We have had so much rain lately I don't know whether to open or close the windows! I was reading about an interesting thing they do in Germany called luften - I might do a post about that if someone hasn't already.
    • CommentAuthortony
    • CommentTimeOct 6th 2020
     
    my frame would be like an architrave very nearly touching the boiler casing
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