Laying chipboard on floorboards, or the joist, and to use insulation or not

Hi You have the choice to remove the old floorboards which will give you the opportunity to insulate in between the joists underneath and then you could fit new tg4 chipboard (or plywood) over the joists again. The best insulation to use is a product called PIR Insulation which comes in 8x4 sheets, which you can mark and cut to fit between your joists, it offers one of the best u-values on the market without having to use overly thick sheets in comparison with the likes of fibreglass roll out insulation, you can search the web for Celotex, Kingspan, Xtratherm etc for more information and they all will have a technical helpline. The issues you may face with this, however, is that sometimes the floorboards, especially in old houses can be very difficult to remove and you will need a skilled tradesmen to make sure this is done safely without effecting other joining rooms in your home. Also when you remove the floorboards you may find a spaghetti junction of electrical cables and if you do you will need a qualified electrician to ensure the insulation fitted is safe and not going to cause any cables to overheat and start a fire. This option really depends on how much you really need to insulate in this area of your home. Traditionally and through building regulations, the insulation requirements is in your roof space, walls and ground floor, and although you do not have a cavity in your walls...you can stud out the inside walls, insulate and plaster over to keep the heat in. There is also the option of purchasing external wall insulation, although this is very expensive. Or if you still really want to insulate between floors, it may be an easier job to insulate the ceiling of the room below with a Thermal Liner product (if you have the headroom), this product is a PIR insulation with plasterboard stuck to it, it is fixed to your ceiling and then plaster skimmed after. Again you could ask for information and a price from a skilled insulation fitter/plasterer etc. If I was you I would study how heat is lost in your home before making your decision as you could be just throwing money away with very little benefit. You are right to avoid fitting carpet on floorboards with such large gaps. If the existing floorboards are structurally sound, you can certainly keep the old floor in place and sheet with 18mm tg4 chipboard or if you can afford it, a hardwood throughout plywood. I would employ a joiner for this job so it is done properly. You will then have a completely smooth surface to have the carpet fitted. Providing the floorboards are structurally sound I don’t really see the need for 18mm tg4 chipboard and would be best with 5.5mm, 9mm or 12mm hardwood throughout plywood (WARNING....DO NOT USE CHEAP HARDWOOD FACED PLYWOOD AS THIS IS NOT DESIGNED TO BE CUT AND IS ONLY TO BE USED IN FULL SHEETS), again you can get the correct advise on what to chose from the tradesman who sees the condition of your existing floor. If he tells you the floorboards are rotten with woodworm for example it is best just to get them lifted and have your house sprayed for woodworm before you take on any other work as this is a very dirty job. In fact I would be asking to see the woodworm certificate for the house. Also take into consideration of the heights of your options, fitting 18mm chipboard, then a 12mm underfelt and a thick pile carpet for example, you may have to ask taller people to duck before they hit their head off the ceiling lol. Essentially you have a few options but would be best finding someone who can inspect visually and offer you the best way forward. Hope this helps Steven

Yes,you can nail the chipboard on top of the floor boards.No need to remove old ones.Also you don't need to insulate as the carpet should have underlay (9mm) laid first.