Venting dry lining on solid brickwork to outside?

Blisterman

I'm looking at internally dry lining a solid brick wall on a terraced house.

The builder recommends creating a 50mm cavity between the existing wall and dry lining on studs, making the inside as airtight as possible with vapour barrier and taping at joints. We looked at breathable insulation, but it just wasn't cost effective.

My concern is mould building up on the inside face of the brickwork, for, no matter how airtight you make it, there will always be some warm air leaking through, and potentially condensing on the cold wall face.

To prevent this, I was thinking of installing air bricks at the top and bottom to allow for some air movement between the 50mm cavity and the outside, so if any moisture does come through, it will be able to dry out and vapour escape.

Is my thinking on this correct?

BryanF

1. What breathable insulation systems have you looked at?

2. how air-tight can you realistically make a drylining system in an existing dwelling?

3. And will venting the cavity just make the house an even draftier ice box?

4. Have a read of the ‘breaking the mould series by j. Little in ‘construct Ireland’ from about 10 years ago

5. What is the age of the dwelling?

6. What is the wall build-up?

7. What is the ventilation strategy?
8. How is the building heated?
9. The insulation options you looked at - what were the prices v what is currently being proposed?
10. Does the current proposal and forming/making good the vents really save that much?
11. Has an arch or eng looked at this for you?

Blisterman

1. What breathable insulation systems have you looked at? - Calsitherm and Pavadentro

2. how air-tight can you realistically make a drylining system in an existing dwelling? - Reckon 4-5 m3/hr/m2, so not especially air tight, but a big improvement.

3. And will venting the cavity just make the house an even draftier ice box? - Ideally the vast majority of air movement will be between outside and the cavity, rather than being between the cavity and the inside.

4. Have a read of the ‘breaking the mould series by j. Little in ‘construct Ireland’ from about 10 years ago - Yes, and it seems to indicate that any approach I take to internally insulating will have damp problems. It doesn't cover a ventilated cavity though.

5. What is the age of the dwelling? - Over 100 years.

6. What is the wall build-up? - Plaster internal finish on Solid brick work. The plaster is not easily removable. Another reason we're

7. What is the ventilation strategy? - MHRV

8. How is the building heated? Underfloor heating

9. The insulation options you looked at - what were the prices v what is currently being proposed? Pavadento and Calsitherm both require a very arduous amount of hacking off the existing plaster, as well as several coats of levelling and finishing lime plaster which is overall costing over €10,000.

10. Does the current proposal and forming/making good the vents really save that much? Yes, considerable savings.

11. Has an arch or eng looked at this for you? Yes, but nobody is really an expert and I'm getting very conflicting information.

booooonzo

in a similar situation.
my understanding is that cavity you create and vent has essentially made the only thing between you and the outside a 50mm insulated slab or whatever it is you dryline with.

we have decided to go with hemplime.

calci and woodfiber was indeed very expensive

have you cement render internally or lime?

how arduous would it really be? if you can go right back to the brick a small sds drill with a chisel will make light work of it.. then shutter/tamp the hemp lime your selves and get a plasterer to finish

Calahonda52

Venting the cavity is just creating more holes in your walls and if you do it, and don't add enough insulation on the inside, including around window reveals, you may well not meet the building regs which apply if this is regarded as substantial work, or whatever the clause is in the new regs.

My understanding of Calsitherm is that it is a moisture management product as well as an insulation
Interior calcium silicate thermal insulation, mould prevention and moisture control board.
https://www.ecologicalbuildingsystems.com/product/calsitherm-climate-board

The ideal scenario is that it is used as part of a fully breathable structure.
.
However its moisture absorbing characteristics are such that when the atmosphere is damp, it absorbs a lot of water: I have some here and a small square will absorb a full glass of water and still not feel wet: my grandkids, when younger, described it as the stone drinking the water.

Then when it is a dry atmosphere, it releases the moisture.

The key here is the properly designed, installed, commissioned and maintained MVHR: all 4 must apply, its not à la carte.
This, and the proper positioning of supply and extract ducts, will be key to vapour control.

Depending where you live, you might look at some sort of dehumidification in the unit if it gets very humid in summer.

hochnie

I will be interested to hear updates on this as I am thinking about similar for a stone structure I will be doing next year.

How thick are you going with the hemplime? the supplier suggests the thermal mass may actually improve the energy efficiency in tandem with the 600mm stone wall.

I have seen a tradical example online somewhere where instead of using a standard frame they just fit battens and screwfix the shuttering adjusting the screws based on a laser level to get a perfectly vertical wall. wall ties into the stone for securing the mix. I think I would be worried with this approach and might stick to a standard frame as I have to go up to near 7metres at one gable.

I am a bit worried about the possibility of moisture migrating to and rotting the hemplime.

booooonzo wrote: »

in a similar situation.
my understanding is that cavity you create and vent has essentially made the only thing between you and the outside a 50mm insulated slab or whatever it is you dryline with.

we have decided to go with hemplime.

calci and woodfiber was indeed very expensive

have you cement render internally or lime?

how arduous would it really be? if you can go right back to the brick a small sds drill with a chisel will make light work of it.. then shutter/tamp the hemp lime your selves and get a plasterer to finish

BryanF

Read up about hemplime. The whole point is hemp binds with the lime mix, the same way cob does. There is no risk of rotting. This is a breathable insulation approach suitable for conservation projects or homes built pre-cement

hochnie

From what I have read it seems to be able to manage the moisture on its own when done correctly, I am just looking at the base of the internal walls after stripping the cement plaster off and they are pretty damp.
This is going to require some work to remove this moisture as the floor level is a metre below the external level in spots.
I will be installing French drains as deep as I can safely go and I am also considering tanking the wall below ground level externally but I am not sure if this is advisable?
I am also thinking about using expanded glass foam for the sub floor insulation here to negate the movement of water from the ground into the walls but I am not sure how this will work in conjunction with a radon membrane as it seems to defeat the purpose of capillary break.

BryanF wrote: »

Read up about hemplime. The whole point is hemp binds with the lime mix, the same way cob does. There is no risk of rotting. This is a breathable insulation approach suitable for conservation projects or homes built pre-cement

BryanF

If your external ground level is a meter higher than internal floor level.. you’ve a few things to sort before considering hemplime

hochnie

Yes indeed the walls will be done next year after I have sorted the roof,floors and french drains etc- tbf its only the back third section of the structure that is below ground level which I am considering keeping as a utility/garage space so I am not unduly worried....yet