crawlspace draughts robbing heat from house

batman1

Ok,
hopefully it uploads.

My problem is the severity of the draughts cooling the upstairs and under the floor . I don't want to make the house airtight, as that is going to take a lot of work and expense. I would however like to try and reduce the draughts to make the house more comfortable while at the same time increasing the level and quality of insulation.

The sketch is crude as I'm no draughtsman but I think it explains the current layout.

sas

Ok, so where is the draft being felt that you are concerned about?

Obviously the crawlspace is going to be very cold and drafty because it's effectively outside.

Is your concern that the draft is passing through the insulation that is on the flat and in the dwarf wall? This could really reduce it's effectiveness.

batman1

sas wrote: »

Ok, so where is the draft being felt that you are concerned about?

Obviously the crawlspace is going to be very cold and drafty because it's effectively outside.

Is your concern that the draft is passing through the insulation that is on the flat and in the dwarf wall? This could really reduce it's effectiveness.

Yes, my main concern is the cold air from that space removing any heat generated very quickly. With the floor joists open to this crawlspace, it's robbing the heat from between the floor plus all the heating pipes are under there for upstairs so it must be affecting their performance too.

I would like to reduce the effect of the cold air from the crawlspace robbing the heat from upstairs. I know it's not a simple solution but if a better quality or more dense insulation was used would it help. I was thinking if I blocked off between the joists under the dwarf wall line that would improve
Things as well.

sas

batman1 wrote: »

Yes, my main concern is the cold air from that space removing any heat generated very quickly. With the floor joists open to this crawlspace, it's robbing the heat from between the floor plus all the heating pipes are under there for upstairs so it must be affecting their performance too.

I would like to reduce the effect of the cold air from the crawlspace robbing the heat from upstairs. I know it's not a simple solution but if a better quality or more dense insulation was used would it help. I was thinking if I blocked off between the joists under the dwarf wall line that would improve
Things as well.

Hi, if I were you'd I'd askt he mods to splinter this off into it's own thread.

Anywho....

What evidence have you to support your theory?
I reckon you are correct but I'm wondering why specifically you think it's this?

Ultimately what it sounds like is that you need to wind tighten your insulation both on the floor and wall of the crawl space.

I've heard of sheets of brown paper being laid between layers of fibreglass to prevent breezes blowing through the insulation and reducing it's effect.

batman1

Maybe the mods would help me out be splintering it off as it's mixed in with the op's thread which he seems to have resolved.

My theory is based on experiencing the cold air myself in this area. On a cold windy day I can really notice the difference upstairs. Downstairs is not too bad except for it cools quickly, especially if it's windy.

I have seen threads about the paper between fibreglass alright. The crawlspaces have fibreglass in them already albeit badly fitted and sagging now. Fitting insulation correctly in this space is very difficult due to dormers and other irregular timbers and shapes.

I was toying with sprayfoam the same as the op's idea but after reading and taking on board sinnerboy's and others knowledgeable posts I have decided it's not the best option for my house.

I have thought about using the foam from wallplate, between the joists to the bottom of the dwarf walls and then up the back of the walls to where the slope starts again while maintaining the ventilation from the eaves right through to the attic. This, I hope, will remove the risk of condensation from spraying onto the underside of the rafters while also reducing the draughts coming from the crawlspaces and travelling under the floor and into the rooms upstairs.

Also, behind the sloping ceiling upstairs there is fibreglass 'suffed' in. This I would like to change as there appears to be no 50mm gap above it. I am trying to see what I could put in there instead that would be a decent insulator but less thick than the fibreglass in order to get the ventilation gap opened up again. I'm not concerned about the attic as I can replace the fibreglass there with new stuff to 300mm.

Poor Uncle Tom

I have moved some posts from the spray foam thread to here on request.

olympicweights

This is a typical issue with dormers. I have one myself. I have started to remedy the problem essentially by building a roof inside the roof.

The plasterboard was stripped off along with the fibreglass to expose the rafters and felt. I then lined the inside of the rafters with a breathable windtight membrane creating the ventilation gap down to the soffit vents, this needs to be cut between all joists and sealed to the wallplate or cavity closer and the same needs to be done at the ceiling joists with the membrane being sealed to the foil backed ceiling slab. This will keep the wind out.

The next step was to run new rafters (3*2) from floor joists to ceiling to created a void of up to 300mm. This was then lined with intello and treated the same way as the breather membrane was at all junctions. This void can then be filled with cellulose and can be achieved with little cold bridging. Obviously dormers create obstacles as do roof windows.

Doing this brings all your plumbing/heating run pipes into a warm area instead of out in the cold crawl space. The down side is that it is hugely labour intensive and really for someone that enjoys diy!

The result is a far warmer room with an even temperature.

batman1

Unfortunately I'm not great on the diy side of things. I wouldn't be confident enough to tackle that big a job. Well done though. Dormers are a nightmare.

I think getting the crawlspace floor and behind the dwarf walls done with foam might be the best solution in my case. I cannot see any issues if I maintain the same level of ventilation as exists already.

Replacing the fibreglass behind the slope is something that needs done but what to replace it with without tearing the ceiling down?

olympicweights

batman1 wrote: »

Replacing the fibreglass behind the slope is something that needs done but what to replace it with without tearing the ceiling down?

The easiest option would be to cut insulation board to fit between the rafters. If you have 150mm rafters you could fit in a 100mm insulation board or 2*50mm boards. You would have to try and slide them up or down from the attic and hope that your rafters are parallel. Not an ideal solution but better than the fibreglass. To ensure you have maintained the ventilation gap use a 50mm waste pipe or similar to push the insulation to the plasterboard side.

batman1

olympicweights wrote: »

The easiest option would be to cut insulation board to fit between the rafters. If you have 150mm rafters you could fit in a 100mm insulation board or 2*50mm boards. You would have to try and slide them up or down from the attic and hope that your rafters are parallel. Not an ideal solution but better than the fibreglass. To ensure you have maintained the ventilation gap use a 50mm waste pipe or similar to push the insulation to the plasterboard side.

I thought about that but I think I read on here somewhere that the rigid insulation is not breathable which might cause condensation. I suspect the rafters would not be parallel so there could be lots of gaps etc.
Was thinking of Rockwool roll or similar that would be thinner than the fibreglass but as good an insulator or nearly as good. I might be best just to leave the fibreglass in place.