Air tightness / insulation strategy for 1990s remodel project

[embra]

Hi folks,

 

We're remodelling our ~1990s built two storey, end of terrace home, and I'd like to establish some simple practical guidelines that can be followed by our builder and myself to improve energy efficiency.

 

I’m looking for advice on 1) air tightness, and 2) insulation for our external walls. I’d like to focus on simple and practical solutions that we can relatively easily implement.

 

The underlying work for our builder is to reconfigure the layout involving some light structural changes, and construct a porch area (all on ground floor of property). We're having the heating system pipework upgraded to suit low flow temperatures and fitting an ASHP.

 

I'm getting anxious that I'm missing an opportunity to make improvements now, as we won't have the appetite at a later date. It's almost certain I'm overthinking this, and hoping advice from others who have done something similar will help. I’d like to understand achievable air tightness and wall insulation improvements that we can intercept at this point, while keeping incremental project time and cost to palatable levels. Any disruptive works (e.g. plasterboard off) would be constrained to ground floor initially, and could be extended to first floor as a phase 2 at a later date.

 

Construction materials are:

 

Ground Floor

Current: Uninsulated beam and block, battens, chipboard deck.

Plan: Lay DPM / PIR / floating floor deck on top of beam and block. 

 

First Floor

Current: Chipboard deck suspended on timber joists.

Plan: Nothing so far.

 

Walls

Current: Brick / cavity / block walls with some questionable looking EPS boards in the cavity. Dot and dab plasterboard on the inner block.

Plan: Help! 😬. Read a lot of conflicting information about whether internal insulation is suitable, not sure if we have the time / budget to make air tightness improvements that will actually be worthwhile

 

Roof

Current: Pitched roof / cold loft, around 100 mm wool insulation already laid.

Plan: Increase to ~300 mm wool insulation.

 

Windows / Doors

Current: Original (~35 years old) 2G timber units, with trickle vents.

Plan: 3G timber units, no trickle vents.

 

 

Air tightness strategy:

 

Easy (current thinking / approach)

• Illbruck expanding air seal in gap between skirting and plasterboard (ground floor, and ceiling joint of first floor from loft. Seal up any holes in the external brick with mortal, and blocks with expanding air seal. 
• Tape ground floor DPM to plasterboard, and cover with wet plaster / skirtings. 
• Tape all window / door openings, skim with wet plaster. Seal gaps around frames with expanding foam strip.
• Seal around any penetrations for services / sockets / light fittings etc with expanding air seal. 
• Make sure brick / block cavity is closed at top of leaf in loft space.
• Remove shower / kitchen extractors that are currently ducted directly outside. Install MVHR positioned in loft.
• Remove other causes of drafts (gas fireplace and boiler flue, cat flap, penetrations for TV aerials, etc...)
• Caulking (or is there a better product) around all internal plaster corners
• Fit draft strips / insulation to loft hatch
• Re-glue joints in first floor chipboard deck (not really sure if this helps)

 

Medium

???

 

Hard

• Remove all internal plasterboard. Fit air tight membrane / boards. Remove plasterboard / floor deck to enable taping around first floor joist / wall junction. 
• Fit insulated plasterboard, skim with wet plaster. 
• Fit vapour check layer and air tight membrane in loft at joist level, fully tape joists etc.
• Probably need a professional to design the details

 

 

Happy to hear everyone's thoughts and advice 🙏

[TonyT]

Heat loss calculator on proposed remodel works will give you design info for the ASHP.

 

You will need to specify tape and means of sealing with a specific product or the cheapest/ most available product will be used and the builder will have complied with the spec unless further detail is given.

 

 

What about PV cabling

What about EV cabling, but these easy to install while remodelling works take place generally harder later..

 

 

 

Just adding thoughts, good luck!

[embra]

Hey @TonyT thanks for the comments and tips!

 

I've prepared my own heat loss calc which was a useful baseline to compare to that coming from heating engineer. My (more on the optimistic side) estimate puts us at ~5kW design case, whereas his draft model is more like 10kW! There are some obvious points of difference in there (e.g. he has not accounted for new insulation we're adding, new windows etc). We're going through in detail next week so hopefully we can come to a sensible agreement and avoid over speccing the system.

 

Are you aware of any guidance on specific products, or a go to spec that I could use? 

 

Have included space in a riser duct for PV cabling (will be installed after building works). I hadn't really thought of EV cabling, since our meter / consumer unit is in our garage and I assumed it would be a simple case of running a cable to the driveway which is immediately outside the garage. Am I missing anything here?

[Iceverge]

On 18/06/2023 at 10:30, embra said:

Plan: Lay DPM / PIR / floating floor deck on top of beam and block

Good

 

On 18/06/2023 at 10:30, embra said:

Current: Brick / cavity / block walls with some questionable looking EPS boards in the cavity. Dot and dab plasterboard on the inner block

 

Closed cell foam to top up the cavity. It'll do a cracker job of improving your airtightness too. 

 

On 18/06/2023 at 10:30, embra said:

Plan: Increase to ~300 mm wool insulation

 

Blow in another 300mm of cellulose. It'll help with airtighess much more than mineral wool, you'll get better coverage around roof timbers etc and it involves none of the human suffering. 

 

On 18/06/2023 at 10:30, embra said:

3G

 

Consider good quality uPVC. Better performance and less cost. 

 

 

 

Think about ventilation.  Depending on access a central MVHR would be ideal but dMVHR/DCV/MEV/PIV would all work. 

[embra]

On 07/07/2023 at 10:41, Iceverge said:

 

Closed cell foam to top up the cavity. It'll do a cracker job of improving your airtightness too. 

@Iceverge are you aware of any sources of information to read up on this? In theory it sounds like a good solution, but I can't find any practical examples that could help checking suitability and plan the execution.

[Iceverge]

If you look for Walltite and Isothane closed cell foam there'll be some documentation. 

 

It's about 5 times the price of bonded EPS beads hence its rare use but it is an option.