After talking it about it for a long time, the cold weather of a week or so ago finally stirred me into action; no number of rugs on the floor would cover the drafts; in previous years I'd covered the floor in hardboard, which is a start, but only a temporary solution. I'll bodge for a while, but things havw to be done properly eventually.
First job was to have a quick look under the floor to remind myself what I had - which was 3 1/2 " across the room, supported lengthways at approx 4' interval by cross members. I did a bit of poking around the internet, and also spoke to Kingspan, who recommended their TP10 polyurethane board, the standard insulation board I've seen all over the place, used on boats, too. In retrospect it would have been easy enough to order board thicker than the joist height (say 100mm, or more) and cut slots to go over the supporting beams, but that didn't occur to me at the time, so I ordered 75mm board from castle Timber in Acton. A bit of measurement suggested I'd need around 4 8x4 sheets for the front room, so ordered 10, to cover the hallway and back room too. The kitchen and bathroom are in the house's rear extenstion and have a solid concrete floor, so that'll need a different approach, another time.
First job was to pull up all the floorboards, after clearly labelling them. I used letters across the room, and numbers long each floorboard were they had been previously cut (for heating installtion etc), starting from the two straight walls of the room (i.e. opposite bay window & chimney breast sides). For pulling up boards I found a crowbar (with nail pulling 'v' at one end) very useful, along with a claw hammer and large flat bladed screwdriver. The first board is the worst to get out, of course. Being built as an 'artisan's' house, the boards aren't of great quality, and a couple were split near the edge from the nails - these can be glued together later.
Pic above shows a cleared section, showing the cross beams at the edge of the room as well as at thirds across. I got away with leaving the short boards in each side of the chimney breast (where most of the junk in the room sits - books, hifi etc.
At this point I also added a few cables I wanted to hide under the floor - the broadband router sits in the corner of the room by the phone point, and I've put in a few cables to other rooms 'just in case'. I also have an extension speaker cable to the kitchen, as I'm sad like that. ;-)
The insulation as delivered, a neat excuse to show the house too... ;-) The boards are pretty light, and easily moved by one person.
A fisheye picture of the cleared room taken through the front window. I say cleared the just either side of the fireplace is visible, as is th sofa - it came with the house fifteen years ago, it's longer than the door is high, and wider too - I have managed to get it out of the room before, but I managed to work around it this time, leaving it on it's end in a corner.
One vital job was to ensure the ventilation under the floor remained - the three ventilation points at the base of the bay window were cleared of accumulated soil. Had I insulated right up to the wall at this point, they would have been partially blocked, so the solution was to build a box over them, keeping a clear air passage free. The joist supporting the boards in the bay window had seen better days anyway, so a handy skip around the corner provided some second hand 3" deep studding and 1/2" ply - perfect, you can't beat a loft conversion skip for such things. I also found a couple of 8' x 2' chlipboard flooring boards from the same skip, which proved invaluable as temporary supports across the joists when putting in the insulation. Anyway - new joists in situ - air channels are in the middle wall, and on the sides (side one visible between the two new joists):
with with ply 'lid':
This was screwed down, and sits at the same level as the joist tops.
The insulation was very easy to cut with an old panel saw; the gaps between joists were largely uniform, but each one needed measuring at each end, as gaps varied between 31 and 34cm, largely around 33. It was easy enough to cut eacvh strip top be a push fit, where too tight I'd taper the side slightly rather than taking it off all the way down. I was able to push it under the remaining alcove floorboards with no problem, occasionally needing a little support from underneath to lift it on to the far cross member.
(note use of chipboard flooring panel as working platform - the job would have been difficult without it).
I also decided to tape over the edges of the board where it meets the joists, and where two sections meet, using cheap black cloth tape, to avoid any tiny drafts getting through. I also used some spray expanding foam where necessary - around radiator pipes, and also around the edge of my air brick 'box'.
I failed to take a 'before' picture with the boards labelled, but this one gives the idea as the boards go back down. I haven't nailed them back down yet, as I want to glue the split boards (clamped in a workmate type folding bench, so I can only do one at a time).
The proof in in the heating - the room was always difficult to keep evenly warm with the drafts previously, and now it warms up nicely, and stays warm, too. I don't like overheated rooms, and the lack of drafts makes a lower ambient temperature fine - I don't tend to run the heating much anyway.
Hallway and back room still to be done, but this was the priority and was well worth it. Could probably be done as a weekend job, especially with more than one person, depending on all the variable factors you can't predict. Definitely doable by someone with basic practical skills and a minimum of tools, too.