Room by room "semi deep" retrofit.

peter_dublin

Hi all.

Wanted to get your feedback on the below. I recently purchased a 200sqm four bedroom detached house which is early 2000s build with a cavity block construction. To say the gas bills are crucifying is an understatement. While moving a ensuite we discovered the side walls are just insulated with 60mm batons with fibre glass between and a VCL over it. The front and rear walls of the house are dot and dabbed with reveal board, so in effect there is 10mm of polystyrene insulation on the front and rear of the house. While the downstairs floor is concrete floor the first floor is timber. As we removed the coving we also found that none of the timber flooring or plasterboard ceiling slabs meet the external walls. In effect there is a 10 - 20mm gap around the external parameter of every room either venting into the floor void or directly into the attic.

As we cannot afford to move out and have a full deep retrofit done we will have to tackle it room by room.

The current thinking was as below and I'd appreciate any comments / recommendations.

Side walls:

1. Strip external walls back to block work.
2. Seal the block work with Blower proof.
3. 60mm of PIR sealed to the floor and ceiling junctions with passive foam. Tapped with foil tape etc.
4. New metal studs in front filled with 70mm rockwoll and all services run in this new cavity.
5. Soundbloc plasterboard slabs.

Front and Rear:

1. Strip external walls back to block work.
2. Seal the block work with Blower proof.
3. Seal current windows to blockwork with airtight tape. Currently there are 20 - 60 mm gaps.
4. Seal Floor to Ceiling joints. (Tape or Foam)
5. 62.5mm insulated slab again sealed with passive foam.

Attic: Add another 300mm of Fibreglass (2 x 150mm) layer

First floor ceiling void will be treated with Blowerpoof and 120mm PIR sealed with passive foam.

We are also considering cutting back all first floors 60mm to have a continuous PIR layer from ground to ceiling rather than have it broken by the ground floor ceiling and first floor timber floor.

Any feedback would be appreciated.

Sleeper12

I'd be going with 100mm wall insulation. Bathroom and box room might struggle with 100mm so 65mm there if 100mm isn't possible. Detached house means most if not all rooms have two outside walls. Can't see you getting away with less than 100mm

Minimum standards for attic is 300mm to the eves Inc under the cold water tank. The tank itself & pipes should be insulated. Vents are needed in the roof tiles front and back. A roofer will do this in so minutes or so. I actually have 400 or 450mm in my attic attic door was changed to an airtight folding stairs with built in foam insulation

ted1

why not just externally insulate the walls ?

There are now loans which should cover the cost and the repayments covered by savings

https://www.seai.ie/news-and-media/home-upgrade-loan-scheme/

peter_dublin

https://www.boards.ie/discussion/comment/122194745#Comment_122194745

We don't have or want to loose the the space, if we externally insulate to a decent level you wouldn't be able to even get a wheelie bin or bike down the side entrances plus the upfront cost. It's a decent size house but they crammed them to maximize the amount of them. Also given that the existing gaps between the floor and ceilings into the floor void and the attic I was concerned the heat wouldn't even reach the external leaf.

peter_dublin

https://www.boards.ie/discussion/comment/122194770#Comment_122194770

Thanks, I had considered replacing the 70mm Rockwool in the new stud with PIR to give a total of 130mm PIR but retained it for sound insulation benefits over more PIR.

peter_dublin

https://www.youtube.com/watch?v=9V2lv0SRIG8

This is the construction we were looking to replicate except the PIR layer is continuous.

whizbang

Pointless external insulation with cavity block.

Absolutely must cut back to floors to get a continuous layer. Dont cut back the ceiling Plasterboards, its needed for fire resistance; get the new plasterboard tightly fitted to the existing ceilings.

Look closely at the airtight layer. In most cases the majority of the sealing is in the finished surface, so sealing the raw blockwork may be unnecessary. If you are taping the joints in the PIR, an extra layer is not needed.

DC999

https://www.boards.ie/discussion/comment/122219325#Comment_122219325

Why 'Pointless external insulation with cavity block.'? Asking for my understanding, not challenging the logic. My basic understanding was any external insulation will retain the heat irrespective of the type of wall and that the wall becomes part of the 'internal envelope'

Lumen

https://www.boards.ie/discussion/comment/122222546#Comment_122222546

….

https://www.boards.ie/discussion/comment/121623797#Comment_121623797

KungPao

I am doing this very thing. We have a cavity walls, and cavity block walls. Yes, the gaps are/were crazy in mine too, a route for cold air to fall (or warm air to rise) all the way from ground floor, up to the floor void, to the attic. Madness.

I am obviously sealing this up when back to block…silicone for the narrow sections, ex foam for larger, and taped over.

The cavity block walls are same as you. I take out the fiberglass roll (next to useless for external walls) and replace with 60mm PIR, jammed in between timbers and ex foam any gaps. Joints taped over with aluminium tape (watch this, some are crap and basically the same as box tape, I use Diall from B&Q actually metallic and very sticky). Then over that goes insulated plasterboard - PIR or Phenolic if I can get it. Use whatever thickness you can fit. People may say 'sure use 100mm minimum total' but that's often not possible if door frames are adjacent or it's a stairs wall etc. 60mm PIR plus even 26.5mm insulated PIR plasterboard will be a huge upgrade to crappy fiberglass and normal plasterboard.

Cavity walls (which have polystyrene boards in cavity about 30mm only), again I put the max on I can fit, 37.5 to 62.5mm so far, and I parge these blocks and make them as airtight as I can as there'll only be one layer going on. Possibly overkill, but best to do it while you can I suppose.

I am also cutting out 60 mm of floorboard and then blasting down ex foam and before it cures sliding down offcuts of PIR or insulated board I have knocking around, then fill gap between this and new wall boards with foam.

It's a pain of a job, but I am enjoying it too, good to know there's no gales blowing behind my plasterboard. Very noticeably more stable temp in the rooms I've done. Not freezing when cold out and not too warm on a nice day like before.

Just remember when done to pay attention to ventilation. What was once a draughty 'plasterboard tent' should be quite airtight for a refurb. I have always on MEV.