Internal or External insulation

BoardsMember

1920's house refurb.

We have to re-write throughout, and we're interested in looking at MHRV so air tightness needs to be considered as part of the project.

I know that external insulation might more performant, and that with internal insulation there are space costs.

But considering we'd need to put up airtight membrane internally for effective MHRV, and would have to put boards on top of that, would we be better off using internal insulation approach? Rooms are reasonably large, with high ceilings so could cope with space loss.

Appreciate feedback, and ideally suggestion of products for air-tightness membrane and internal insulation.

Thanks.

Calahonda52

before discussing what might be the optimal solution here you need to provide much more information on the exact makeup of the walls, floor and roof.

The reason for this is that 1920's construction needs different considerations to more modern construction.

What else are you doing to the house?

Where is the house: rural or urban, sheltered or exposed?

What external downpipes, sewer pipes etc are on external facades?

What's the proposed methodology for what I presume is rewiring?

Where did this come from:
we'd need to put up airtight membrane internally for effective MHRV

BoardsMember

Thanks for your response. I will try to answer your questions below...

before discussing what might be the optimal solution here you need to provide much more information on the exact makeup of the walls, floor and roof.
The walls are original walls, 1920s part redbrick, I'll have to dig out the original survey, I'm not 100% sure what the construction is. Concrete soffits.

Original roof, no membrane below the tiles, I insulated with a layer of rockwool between the joists some years ago. The attic level is not flush with the top of the walls of the house, the upstairs rooms have high ceilings because at the front and back they slope up at the sides, so stealing extra height. Not sure if I have explained this correctly.

The downstairs floors are the original floors, so are suspended wooden floors in the tow living rooms, with a solid concrete floor on the return. This is a massive source of drafts as we do not have carpets. We intend to address this by either filling in the cavity, pouring concrete, and laying UFH OR insulating between joists. Costs will largely determine which decision, we have a QS looking at it at the moment.

What else are you doing to the house?

As well as rewiring and looking at the insulation, we are also building a side extension, circa 40 sq metres, by knocking the garage & knocking out the back reception room wall.

Where is the house: rural or urban, sheltered or exposed?

Urban, end of terrace, Dublin 6 area.

What external downpipes, sewer pipes etc are on external facades?

There is one to the side at the very front that would not be affected, just for the gutters. There are two on the return, one for waste from the upstairs bathroom, one for water from upstairs bathroom. One of them also takes rainwater.

What's the proposed methodology for what I presume is rewiring?

I'm not really sure what you mean. We have the old type board, screw in fuses. I believe the sockets were earthed in reasonably recent times, but the wiring needs to be done throughout, new board, all new wiring.

Where did this come from:
we'd need to put up airtight membrane internally for effective MHRV

A little information is dangerous! I thought I was right in suggesting that in order to use MHRV you need to tend towards air tightness, and in order to do this, you need to look at adding an air tightness membrane.

I hope I have not muddied the waters further with this post!

Calahonda52

Thanks for the above.
Lets get some more info so as the experts here will have a better canvas to work from

Have you any wall vents on the external walls that will allow you see what the wall construction is:
the reason I ask is that if they are mass concrete, then they are airtight as is.
Are all internal walls solid?
Re the wiring: is it planned to chase the walls or what?
Are you moving meter?

Is existing heating system rads and if so where do pipes come from, floor or walls?

Re the replacement floors: concrete would take forever to dry out.
End of terrace with brick front would probably exclude external insulation as an option

Am not clear on the roof/attic design when you say attic not flush... can you maybe draw a sketch of the cross section and post it, take a foto with fone.

Any plans to replace windows/doors

Have you a draught lobby? aka porch door.

BoardsMember

Thanks again for the response, I'll try to answer your questions as well as I can.

Have you any wall vents on the external walls that will allow you see what the wall construction is:
the reason I ask is that if they are mass concrete, then they are airtight as is.
Are all internal walls solid?

No, I'm pretty sure we do not have any vents. There are fireplaces in 3 or 4 of the bedrooms, both living rooms, and there is an inaccessible vent/hole behind the boiler. There is also a tremendous draft from underneath the floorboards ventilation has never been an issue

We only intend using one into the future, and will fit a sealed stove, the others we will seal/close according to best practise.

Re the wiring: is it planned to chase the walls or what?

Yes, I imagine so, so there will be a good bit of making good. That said, I understand that in the interest of air-tightness, the recommendation is to have as few sockets/fittings on external walls.

Are you moving meter?

We'll have to, it's in the garage which is being knocked down.

Is existing heating system rads and if so where do pipes come from, floor or walls?

Rads, yes, decent boiler, condensing running on gas bought in 2008. Pipes from the floors throughout.

Re the replacement floors: concrete would take forever to dry out.

We could probably fill the cavity with stones (or whatever) and then insulate & pour concrete to the required depth for the UFH, so would not expect it to take any longer than a standard pour when trying to create conditions for for UFH.

End of terrace with brick front would probably exclude external insulation as an option

Only red brick to the front. The gable end and the rear are not red brick, beyond detailing on the corners, so we would probably go for external on gable (including the extension) and to the rear. Would even consider no insulation, or internal only to the front if that did not cause issues. Front is south facing.

Am not clear on the roof/attic design when you say attic not flush... can you maybe draw a sketch of the cross section and post it, take a foto with fone.

I have attached a very basic, drawing is not my strong point, but you should get the drift!

Any plans to replace windows/doors

At the moment no, but we are trying to ascertain how performant they are, they are double glazed windows from early 1990.

Have you a draught lobby? aka porch door.

Yes, the porch is flush with the front of the house, its the same product as the double glazing, installed the same time (white pvc double glazing).

Calahonda52

https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx might help with your deliberations, especially with the floor.

Its 12Mb or so not for the phone!

Good sketch!

What insulation is at point 1 in the attic sketch attached.
[the second attachment is just to show what it looks like in a pre-conversion situation]

Re sockets on external walls and A/T layer, it depends on the wall construction, hence one of my original questions.

The other question that occurs if u go MHVR, where will conceal the ducting and will the unit be inside the insulation layer.

If you used advanced search on google with boards.ie as the domain, and use my moniker and some key words such as MHVR you will find some links to some previous documents I have posted on the subject
eg
http://tinyurl.com/jppcwou

The same idea will work for posts by others who know more about this than I.

Re the location of the A/T layer, have you considered a service cavity inside the A/T layer?

You need to draw a section through the house as you did already and then draw the A/T layer.

BryanF

Op please use the [ quotation ] function. You're around long enough.

BoardsMember

Thanks for the link, I'll read and see what I can understand/take from it.=, and for the suggestion re advanced searching. It can be hard to find the wood from the trees sometimes, often the questions asked/answered are not identical to your own situation, and serve only to further confuse!

I found the original surveyor report we got done before buying, the surveyor reported that the external walls are constructed of concrete blocks and bricks, not sure if that helps a lot.

Calahonda52 wrote: »

What insulation is at point 1 in the attic sketch attached.
[the second attachment is just to show what it looks like in a pre-conversion situation]

There is no insulation there, from the attic you can touch the tiles. There was a layer of lime render on the inside but that is fast crumbling and falling off. So there is no second barrier behind the tiles.

Calahonda52 wrote: »

The other question that occurs if u go MHVR, where will conceal the ducting and will the unit be inside the insulation layer.

I have no idea, I'd have to go with professional advice on this. With that in mind, what I am trying to ascertain with this post is basically the decision points, merits or otherwise of internal/external, what to look out for. We have met a number of builders and architects, and they always come to the table with differing opinions, and are pre-disposed to one approach over another. I'm hoping to just get a fully objective understanding of things here, if nothing else.

Calahonda52 wrote: »

Re the location of the A/T layer, have you considered a service cavity inside the A/T layer?

You need to draw a section through the house as you did already and then draw the A/T layer.

I'm not sure what the A/T layer is, sorry I'm not sure the internet can support another of my sketches though....

Calahonda52

A/T is airtightness layer or automatic transmission, context specific:D

Back tomorrow

BoardsMember

Ok, should have copped that.

I think that we may not be going all guns blazing for perfect A/T, its more to do what can be done relatively easily in order to have MHRV working well. Again, keeping in mind we need to re-wire and improve insulation, I am trying to get an idea of how we could use these as opportunities to also address A/T and MHRV and so not to miss opportunities for improving overall house performance, reduce heating costs etc - just to make smart decisions while we're having a considerable amount of work done.