Everything you need to plan, price and understand your home renovation.

First fix is everything done before the walls are plastered: running cables and pipes, fitting back boxes and building stud walls. Second fix comes after plastering: sockets and switches, radiators, the toilet and sink, doors and skirting.

Waterproofing a wall or floor so water can't get through. In a bathroom it is a waterproof membrane or coating under the tiles in the shower area. In a basement it keeps groundwater out.

How much heat escapes through a wall, roof, floor or window, measured in W/m²K. The lower the number, the better the insulation. New walls in an extension need 0.18 or better under Part L of the Building Regulations.

Building Energy Rating: an energy label for your home from A1 (best) to G. You need one to sell or rent, it is done by an SEAI-registered assessor, and you need a new one after SEAI grant work.

A sealed membrane across the ground floor that stops radon, a natural radioactive gas from the ground, getting into the house. It is required in High Radon Areas, and every new building needs a standby radon sump.

A roof where the insulation sits above the timber or concrete deck instead of between the joists, so the whole structure stays warm. It is the usual choice on a flat-roofed extension because it avoids condensation.

Designs the parts of a build that hold it up, such as steel beams, foundations and dormer frames, with the calculations to prove it. They also check and sign off the work for your records.

Plastering puts a full coat on bare blockwork or new board. Skimming is a thin finishing coat, about 2 to 3 mm, over existing plaster or plasterboard to give a smooth surface ready for paint.

The full scope of work, materials and any allowances (for tiles or sanitaryware), labour, VAT, what is excluded, the payment stages and the timeline. If something isn't written down, assume it isn't included.

A list of small defects found near the end of the job, such as a sticking door or a paint touch-up, that the builder fixes before handover and the final payment.

A small percentage of the price held back for an agreed period after completion, to make sure any defects that show up are put right.

A change to the agreed work after the job starts, such as moving a wall or upgrading tiles. It should be priced and agreed in writing before it's done.