Insulating under the ground floor
Another week of holidaying, well another week spent on the house trying to get as much done as I can, this time insulating under the ground floor.
The idea for this week was to start work on the kitchen diner or is it the family room, I’m not sure, anyway the big room on the ground floor that was originally two rooms but was knocked into one and had French doors added, that room.
Ideally I was going to work hard on it and have something to show for all my endeavours by the time it came to going back to the day job. This could have been the case but plans didn’t start well, I had hoped to get a holiday week a week later than then one I took, but due to circumstances I decided it was in my best interests to take the week that started a little prematurely for my DIY agenda. Basically I could have done with a week free to do planning and ordering of materials, without this breathing space I was immediately up against it as I had to shop and design while I was literally on the job.
My first job was to get organised, all my tools, fixings, widgets, materials etc. were all askew, everything was just lying around in lazy piles there was no organisation whatsoever. So knowing this could have been done in my lieu week I started eating into my valuable holidays basically piling things up, sticking screws into jam jars and getting some semblance of organisation. It took some time all this organising and by the time I had everything neatly stored and structured it was already a couple of days into my working holiday.
Still anyway all my tools were now to hand and while I’d been jam-jarring I’d had the foresight to organise a set of tools to pursue the next job in hand, lifting the flooring.
Once this had been done I needed to remove the paneling from the bay window and the skirting boards around the room to allow access to the floor boards. This was a pretty straightforward job but the paneling did need a rather gentle touch. The rot in the bays had gotten into the bottoms of the paneling and any sudden moves with a crowbar could have caused it to shatter into a dozen bits, so softly softly and the panels were all removed reasonably intact. The damage to them had already been done and although the temptation was to throw them on the fire I resisted and put them to one side for renovation at a later date.
Now floorboard lifting should now be as natural to me as breathing as I’d done so much of it. However all floorboards are not laid alike and these ones were rather superhumanly fitted down, where once there might have been only one nail per joist there were now two and each had been nailed in place by a Victorian nailing god with extra-long Victorian nails and with some Victorian glue to hold them in that little bit tighter – I exaggerate a bit, no glue was used, the nails however were blinking long.
Anyway my first course of action, in an attempt not to damage the floorboards as I’d be using them later, was to use a nail punch to pop the nails through the boards and safely remove the undamaged timber. This would have been good if the nails had simply “popped” through, but unfortunately the reality was a little more exhausting with each nail requiring a good old seeing to to get it through the board, I was actually wellying the punch with such ferocity in the end that it was quite astounding I wasn’t snapping the punches. I decided to seek another solution when upon I inwardly remarked my hands seemed to be getting bigger with all this manual work I was doing, only to realise my hand was bigger as it was swollen from me hitting it so much with my hammer.
The next move was the good old faithful reciprocating saw and long handled lever. The technique was first to cut the ends of the boards off with the saw fitted with a wood cutting blade, this stopped the boards inevitable splitting at the ends when one tried to tease them up. The next move was to walk along the plank with the lever and gently lever the board up at each joist, not too much to crack the board, just enough to allow one to get the saw underneath. Once the boards was proud of the joist for its full length then I fitted a metal cutting bladed to the saw and went along the board cutting through each of the leading edge nails with said saw. Next it was back to the lever and teasing each of the boards up so one could get at the second nails, this was more tricky as the nails were well-deep into the board and getting the saw blade to them was sawing in the dark somewhat. The blade I have is really long and when new and straight, if directed right, it had no trouble in cutting through that pesky second nail but when older, duller and bendier it got a bit more problematic. The rot would start the second a nail was missed and the end of the saw blade was abutted to something rather solid, what was a reciprocating saw became a reciprocating human as the saw stayed firmly put and my arms and shoulders oscillated at 1200rpm. This would make for the bendy blade that would then become much harder to direct into the recesses of the board, making nail cutting far more difficult. Still this technique proved far more successful than the nail punch and I was having a much more positive time of rescuing floorboards without damaging them – well apart from the sacrificial couple of inches at each end I offered to save the boards from cracking as I pried them out.
Getting a third of the room’s boards up proved a lot more time consuming than I’d thought and it revealed more wet rot. The wet rot I’d already noticed when I’d teased up some boards in the bay window earlier in the year. The joist ends had suffered from water seeping into the bays from above, a bit of detective work and some expensive releading/reflashing of both of the bay window’s roofs and this had solved the problem, but the damage had been done. What might have appeared to be wet rot coming in through the walls had been a roof problem – or actually probably a more simple problem with the casement windows (I’d removed) not being closed properly. Anyway the influx of water had been resolved and stopped, the problem now was removing the wet rot.
Reading around there were two acceptable solutions, one being to replace the joists, which I would have done, but unfortunately they weren’t a standard size and the other being to extend the joists using bolts and structural timber. Not a pretty solution but when executed properly it proved to be a more than adequate solution.
To remedy any future potential problems I took a double headed approach, I coated liberally the ends of the joists, old and new, with wood preserver and I then wrapped all the ends of the joists with heavy duty polythene damp proof course. I did realise that the ingress of water had been from above and that there was no evidence that it had seeped in through the foundations, but hey the floorboards were up, the preserver and DPC were reasonably cheap and although it took some time to do, the positioning and joining of the DPC strips being a bit time-consuming and gnarly but it was worth it for the belt and braces comfort of having set good foundations for my work.
The next question was what to do about the floor?
After the success of restoring the big bedroom floor I decided the best course of action would be to pursue rescuing and renovating the Victorian pitch pine floorboards in the new family room. I knew that there would be some wastage due to damage but I felt I could either cannibalise them from another room or purchase them from a reclamation yard. So although a big saving would be made on purchasing a commercial solid floor it would equate to time and effort being spent teasing up the boards and then sanding and finishing them later.
The next job was how to put together the floor?
I’d decided that insulating the walls would be a mistake, it would cost time and lots of money and it would also mean I’d lose space lining each of the rooms and I’d also have to dismantle the Victorian cornicing and hope that it would go back in place without damaging it. The walls though were solid and very very thick and as I’d decided to invest in a state of the art heating system, to thoroughly insulate the attic – the attic had already been treat to more than double the insulation the house had originally been afforded – to fit underfloor insulation between the ground and first floors and to replace the windows with A-rated double glazed top of the range units. Well it was properly sorted now in most areas already but what to do about the ground floor?
The plan was to meet building regulations for insulation in accordance to the rather strict dictum of new build standards. Armed with the dimensions of the room, the perimeter to outside walls, perimeter to inside walls, wall widths, height of void, height of room etc. I got in touch with the very helpful Steven King at Knauf insulation. Steven has his fingers on the pulse of all things insulative and has access to a positively brilliant equation that calculates the insulative qualities of walls, roofs and floors. With the ever patient Steven I spent a number of days emailing him with different designs for floor insulation. Each one concluded that the space between joists wasn’t sufficient to fill with any type of insulation, it just couldn’t be tempted to get to the building standards level of insulation I required.
At this point there were a couple of contradicting voices in my head, one supporting the search for the illusive solution and the other to just ditch the idea and do the best with what we had. Anyway much scouting around the internet and lots of contradicting ideas inexorably led me to a site that seemed to know what it was talking about.
This was ideal, I quickly put together a specification:
- 29mm pitch pine tongue and groove
- 12mm spruce plywood structural timber subfloor (offers up a solid plinth for the tongue and groove, not essential but it allows the tongue and groove to terminate mid-joist – if you get my drift)
- 100mm of Knauf Ekoroll insulation between the joists
- 4mm hardwood plywood fixed to the bottoms of the joists (this is to suspend the inter-joist insulation, most websites recommended using chicken wire but some of the more lofty sites poo-pooed this idea as the wire would often crawl and droop over time and allow water moisture ingress)
- 25mm foil backed PIR insulation fixed to the bottom of the plywood, this fixed a lot of the problems with the joists causing thermal bridging and also the foil backed insulation offered excellent vapour control – see website.
The reply came back from Steven with a big thumbs up that this met building regulatons.
Insulation Results from Knauf – anything better than a resulting u-value of 0.22W/m2K would be the aim (lower the number the better)
Now this wasn’t going to be easy, crawling around on a soil floor wasn’t my favourite way to pass the time, but I felt it would be worth it in the long run.
Anyway what I had thought to be a rather rough few days work turned out to be a much longer exercise and by the end of the holidays I’d only managed to progress about a quarter of the way into the room. What it all involves – yes I like lists today – is:
- Lifting the floorboards, trying not to damage them, the floorboards having been fitted by superhumans in stove-pipe hats. Once lifted all the remnants of the nails need to be removed with an angle grinder with shuttle runs to the smoke detectors when the angle grinder sparks set them off.
- Removing all the rubble and stones from under the floor, I could just leave them there but they are rather uncomfortable when one finds oneself squirming around under the joists fitting insulation.
- Fitting a damp proof course around the perimeter of the room, again not as simple as it sounds as the DPC needs to go into rather twisty corners and under unmoveable joists, this DPC in turns needs to be joined together using rather icky DPC double sided tar-like adhesive tape.
- Cutting the plywood to size and then screwing it to the bottom of the joists. Now I know that I don’t have to squirm entirely under the floor but most of the work does involve lying on ones back on the soil floor with the top half of my body under a gap no more than two and a bit bricks high. This is mightily uncomfortable, dirty and really nasty work. It is my least favourite job I’ve had to tackle on the house so far.
- Cutting the insulation to size and fitting it to an even tighter space, again muchos squirming on the floor in an even neater space.
- Taping the joints between the insulation sheets with foil tape and taping the insulation around the underside edges to the DPC. Really another nasty nasty job.
- Once you’ve done one metre of floor you could find yourself the worse side of three hours of work, so a thirty square metre floor is going to take some time.
It is quite hilarious though, the amount of soil I deposit in the bathtub after every session, it is quite extraordinary. I have invested in a good respirator now as I was beginning to get black bogeys from the soil I was inhaling, I was feeling a little tight chested too, so out went the donkeys years old dust masks and in with a nice new respirator.
Along the way I’d tackled a couple of other jobs, the first had been to remedy the missing bit of wood that the joists had been resting on. This wood had spanned four joists in the bay window and had been the leveling packing that had been used to bring the all up to a horizontal floor. This wood along with the joist ends had disintegrated, in one spot it had completely welded itself to the bottom of a joist in a rotten muddle of wood. In an effort to replace it I stacked a pile of slate cutting underneath each joist, this was the recommended way of doing this, but unfortunately the stacks were a bit unstable and would often fall down. In an effort to resolve this I consulted some building forums and first used an building adhesive to form a cohesive structure and then I further reinforced this by cementing them in, not the nicest thing to look at but solid as a rock and nice and level.
Another little job that needed tackling was to vermin proof the external vent in the bay, the one that was in place was deteriorated and fitted over the nice ornate Victorian vent cover. I purchased some narrow gauge galvanised netting and molded it into a box and cemented it in internally. Again not nice to look at, but externally it is barely noticeable and it is a much nicer solution than the one that had been fitted over the ornamental vent cover.
Actually this is just the dirty start of the job, there’s still a subfloor to fit after all the services have been installed, that’s the electric, the heating pipes, hot/cold domestic water, the AV cables, the networking etc. Then after this is done the tongue and groove needs to be cleaned and sorted before it’s tacked into place and then sanded, varnished and filled.
And that’s just the floor.
So why do this, well it seems to me that although my monster thick walls may prove a bit of a heat sink in winter that the floors may prove much more problematic. Think of it this way, under the floorboards there’s thirty odd square metres of cold air facing onto that floorboarding, cold air that is just as cold as any of the other winter air outside, the only thing between anyone and this air is 28mm of tongue and grooved gappy floorboards, I think I can live with a few weeks of rather dusty work to get this all sorted out with lots of lovely insulation.