Dryline box room

Are the internal walls block walls (Thermal Mass) ? - Are you into DIY ? - 100mm Sheets of Polyiso Insulation are over €60 a pop and each one covers 2.88 sq m. Plasterboard 12.5 mm is around €15 per sheet-

Vapour Barrier €40 then maybe Timber Studs at 400mm centers...

Tools - Tape/Fillers etc etc etc, Do you have to move the Radiator/Electrical Socket?

How long is a piece of string?

No Idea how much a tradesperson will charge but this is a DIY Forum.

OP firstly insulate your attic. See what sort of difference that makes.

I reckon you should be able to get a lad to do it in two days for 600 cash. But that's labour only.

If doing it yourself there are plenty of vids on youtube. Go with at least 92mm inslutated plaster board. It's not rocket science or overly difficult but when you pay a guy to do it you're paying him for the finish so just remember that.

I'd be getting a lad in to be honest.

But don't be expecting amazing results if you haven't done the attic.

good video on the process here:

@C. Eastwood "You will also need to fix 30 mm insulated slabs on to the internal block walls which are connected to the external walls to prevent a cold bridge and prevent a thermal bridge." ,

Is this really needed, What about thermal mass ? In the one room where I added 100 mm to the external wall only all I see is a room that is totally transformed in terms of Comfort and Heat retention, It gets 5 degrees warmer than it did before I put 300mm in the Attic and 100mm polyiso on the external walls.

That's my Plan, I will now move to the other north-facing large Bedroom with an Ensuite, Total cost of Materials will be approx €1,100 - I have all the tools/adhesives/fixings/Pre Mixed Jointing Mud, and learnings from the 1st room and will make it a much easier process - I will then do the last 2 bedrooms (both quite large) that are already warmer as they are in the center of the house and only have 1 external wall. My build-up was 100mm Polyiso. A 100% Taped Vapour Control Layer(Green Plastic) 3x.1.5 Battens on the flat at 400mm centers fixed to the existing wall with 200mm fixings then 12.5 mm foil-backed Plasterboard.I have also improved ventilation in the Ensuite and nearby Family bathroom....

Big rooms help - This is not a 3-bed semi we are talking about, The benefits are well worth the lost space.

Assume an uninsulated external wall and a 100 mm concrete block internal partition built-in to the external wall.

The U Value of the external wall will be approximately 2.0 Watts/M2/degC/hr

If you add 100 mm of insulation on to inside face of the external wall - the U Value will be reduced to approximately 0.3 Watts/m2/degC/hr.

But where the 100 mm partition is connected to the external wall, there is no 100 mm insulation so the U value where the partition abuts the external wall will be unchanged.

Therefore the 100 mm partition is now a Cold Bridge, which may lead to Surface Condensation forming on the partition where it abuts the external wall.

The partition wall should have some insulation fixed on to it to prevent this Cold Bridge.

Your Existing wall has a U Value of approx (50 mm Aeroboard) 0.53Watts/m2/degC/hr.

Adding 50 mm insulation by filling the cavity will reduce the U value to approximately 0.3Watts/m2/degC/hr. This is a very good U value.

With this construction you do not need to insulate internal block partitions abutting the external walls, as these walls cannot constitute cold bridges.

Your cavity constructed concrete block walls with 100 mm insulation would be very good walls for Thermal Mass which is as follows:-

The capacity of a building material to store heat. Materials with a high thermal mass absorb heat, store it and then release it later on. This can help to smooth out extremes in temperature inside a building, helping to maintain a comfortable environment.

Therefore the I00 mm internal concrete block leaf, and internal block walls will absorb heat generated from the heating system, and store the heat, and when your heating is off the heat stored in the internal block leaf and internal block partitions will contribute to heating the building.

The concrete floors will also be good for thermal mass.