Hi CBGB,
There are diverse opinions on upgrading.
Don't automatically plump for internal insulation.
It takes careful consideration to get it right and can actually make matters worse if its done badly, by reducing the amount heat available to help the blocks dry out after wetting.
Certainly consider re-rendering to improve weathering abilities with a water resistant but not vapour resistant material.
Insulating the inside of a house is not a matter of cost alone but consideration of your detailing to avoid making existing problems worse, creating even more cost.
Before you consider detailing you need to consider the specification - what materials are you going to use to achieve the result - and this can be dependent on the existing technology.
The critical details - as in all construction forms - are the following; -
- Rising Wall/Floor
- Floor
- Thresholds
- Jambs
- Sills
- Heads
- Eaves
- Attic
Depending on what you're doing you may also need to give a lot of consideration to
- First Floor Perimeter
- Services Penetrations
I understand by single block you mean 9"/225mm Hollow Block walls.
Its easy to see why you'd be tempted to insulate internally, but you should also consider externally insulating the house.
When you're replacing the windows, allow a deeper frame/an offset hinge to let the external insulation return to the window and not foul outward opening sections.
Ensure the outward opening sections complies when fully opened [especially with the offset hinge] with Regulation Part B required window dimensions for means of escape in case of fire.
Several companies produce do external insulation solutions and some will measure up for and install proprietary cill extensions and will undertake the eaves detail and install ventilators for the attic.
External insulation; -
- avoids having to insulate the first floor perimeter separately - the whole external walling is insulated, including this zone.
- helps to deal with the cold bridge at ground floor level by extending the insulation below DPC level.
- avoids interstitial condensation problems because the structure is all "warm"
- assists with making the whole house weather tight
- does not reduce the internal floor area.
The attic detail is worth taking the time to do as well as you can now.
If you're going to convert the attic at some point and floor it out, now is the time to install the deeper joists for floor loadings.
You can use high density insulation between the roof rafters, sized to leave a 50mm air gap, with whatever thickness remaining to be provided by insulation under the rafters.
This basically continues insulating the "outside" as far as it van be done with a traditional slated or tiled roof. and more of the roof structure is warmer than if all the insulation is at the second floor ceiling level.
Don't forget the ground floor - if you have the head height, install the required depth of insulation - this will affect the thresholds.
Don't forget the chimney - its the single greatest infiltration loss and you should consider closing it with a special damper to allow its occasional use, but also consider ventilation of that room when its not in use.
Don't forget to not install insulation from under the water tank, if you decide to lay insulation on the first floor ceiling - insulate teh top and sides of the tank and all water bearing services pipework - the extra insulation will make the pipes in the attic more liable to freezing.
So as you see its a completely different bill of quantities depending on whether you
A) insulate internally and lay attic insulation on top of the first floor ceiling
-or-
B) insulate externally and insulate the attic space between the roof rafters
This is non-exhaustive general advice.
As in all things that affect building physics, employ a building design professional.
FWIW
ONQ.
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