Solid wall insulation

[Pinkfizzy]

If you have solid walls and have dismissed the idea of insulating them because internal insulation means losing floor space and external insulation is kind of like handing your wallet over and saying, please empty it, the govt is trying to persuade you to act now, via substantial grants under the Green deal.

Unfortunately, said grants have inflated industry prices and made external wall insulators see £££ before their eyes....I have just received 4 eye watering quotes, but more confusingly, every single person rubbished the products of the other companies...and then the builder came along and said, just don't insulate, apart from your loft, as you will lose your natural house ventilation and heat will be trapped inside when it rises, causing it to condense, trickle down & stain ceilings and walls.

Any knowledgeable persons out there, who can help me see the wood through the trees ?

[PigletJohn]

Your builder is wrong.

Condensation comes from moisture and cold surfaces, not from heat.

Certainly you have to ventilate the house, whether or not it is insulated, and if you drape wet washing around the home, or don't have an effective bathroom extractor, or don't open the bathroom windows, it will be excessively moist.

If you do have a moist house, and you put a gallon of water into the air, for example by hanging wet washing on radiators, and you have cold walls, then a lot of the water will condense on the walls, making them damp and mouldy. If the surface of the wall is warm, as a result of insulation, and you put a gallon of water in the air, it will find another cold surface to condense on, usually the windows and the WC cistern, and inside the loft.

However the insulation did not create the water.

[PigletJohn]

P.s.

If you have cold solid walls, then next time your bathroom is refitted or redecorated, look at insulating boards of rigid foam intended for tiling on. Even an inch (25mm) will make a useful difference, though 50mm would be better. If you are DIYing and have no labour costs you can hack off the existing plaster, which in an old house may be very thick. You only have to put it on the external walls.

The foam boards have the insulating power of twice their thickness of mineral wool, so although more expensive, are a better choice on walls. Lofts, being big and roomy, the cheaper wool is better value.

[ParsingFlatly]

The watchwords for an energy efficient house are: insulate, ventilate.

Same principal as wearing woollies and a big thick hat, but still leaving a gap to breathe. And your coat being a breathable fabric rather than a plastic bag.

BTW external wall insulation has always been eye-watering. When I looked into it long before any grants, it was going to cost something like 20% of the value of the house.