I'm due to get a load of waste cleared from under a Victorian terrace subfloor (see my other recent post - counting down the days!). This was the main thing that I wanted doing, and then whilst the floorboards were up I thought it would be good to get the floor levelled and insulated.
The floorboards have been lifted and are waiting for the waste to be taken out. There was some rot to quite a few joists ends, particularly around the bay window and some slightly mysterious looking dampness in a few locations where the joists sat on top of the the floorplate/soleplate (the strip of wood running along the top of the dwarf walls and 'ledge' of the main walls). The joists don't sit in pockets in the walls, but rather there is a ledge that protrudes out which they are placed on. So the condition wasn't as bad as I had anticipated it could be, but room for improvement and repairs required. More airbricks will be added and obviously airflow will be much improved once all the waste is gone. Once things are more visible under there I will probably request that there are some holes put in the dwarf walls etc to allow more air flow within the floor generally.
The main thing was that the floor was very bowed and indeed had already been levelled in places so the builders suggested that, in addition to the repairs that would be needed to the joist ends, it would be more efficient to just replace them all rather than level and repair the existing. There is a little bit of me that doubts whether I should have agreed to that or suggest they maintain as much as possible, but it has happened now so please hold back on the criticism if there is any to be had!
I'm looking for some advice on the method suggested by the builder for reinstating the new sole/floorplate - they have been very good so I think they would be receptive to a change in approach if needed. My description below is what I recall from my discussion with them.
As I understand it they will put a layer of mortar and strip of DPC (plastic of some sort) material along the top of the dwarf walls and 'ledge'. I'm not sure whether it be will be mortar then DPC or vice versa. The floor plate timber strip will sit on top of this, and then the joists will sit on the floorplate. Its essentially a like for like replacement of the set up that was already there, though the joists will be sturdier, save for the addition of a DPC. There might be an existing bitumen damp proof course within the wall itself, but I'm not certain of this.
Things that have popped into my head:
- should I request that lime mortar is used for any bedding in of anything? I think this will only be on the top of the dwarf walls or ledge.
- is a plastic DPC acceptable? I've skimmed through various posts on here and it seems to come up as a suggested option from various people. I'd considered whether to ask for slate or something but it feels like that would just do the same thing.
- ensure that the joists are set slightly away from the walls and don't touch them
I know that subfloor insulation is a divisive topic, and it is making me a little bit edgy. It was mainly a case of, if all the floorboards get lifted to remove the waste then I may as well do this too. Because the joists are being replaced, the floor now becomes a building control thing (they were already having to inspect some work elsewhere in the house) and therefore I'm not sure if I could get away with just not insulating at this point. I haven't actually been on site to speak to the BCO when they've been there in order to have a conversation along the lines of "i'm a bit worried about whether the damp has been resolved and would prefer not to install the insulation right now". This is to be determined.
The floorboards have been lifted and are waiting for the waste to be taken out. There was some rot to quite a few joists ends, particularly around the bay window and some slightly mysterious looking dampness in a few locations where the joists sat on top of the the floorplate/soleplate (the strip of wood running along the top of the dwarf walls and 'ledge' of the main walls). The joists don't sit in pockets in the walls, but rather there is a ledge that protrudes out which they are placed on. So the condition wasn't as bad as I had anticipated it could be, but room for improvement and repairs required. More airbricks will be added and obviously airflow will be much improved once all the waste is gone. Once things are more visible under there I will probably request that there are some holes put in the dwarf walls etc to allow more air flow within the floor generally.
The main thing was that the floor was very bowed and indeed had already been levelled in places so the builders suggested that, in addition to the repairs that would be needed to the joist ends, it would be more efficient to just replace them all rather than level and repair the existing. There is a little bit of me that doubts whether I should have agreed to that or suggest they maintain as much as possible, but it has happened now so please hold back on the criticism if there is any to be had!
I'm looking for some advice on the method suggested by the builder for reinstating the new sole/floorplate - they have been very good so I think they would be receptive to a change in approach if needed. My description below is what I recall from my discussion with them.
As I understand it they will put a layer of mortar and strip of DPC (plastic of some sort) material along the top of the dwarf walls and 'ledge'. I'm not sure whether it be will be mortar then DPC or vice versa. The floor plate timber strip will sit on top of this, and then the joists will sit on the floorplate. Its essentially a like for like replacement of the set up that was already there, though the joists will be sturdier, save for the addition of a DPC. There might be an existing bitumen damp proof course within the wall itself, but I'm not certain of this.
Things that have popped into my head:
- should I request that lime mortar is used for any bedding in of anything? I think this will only be on the top of the dwarf walls or ledge.
- is a plastic DPC acceptable? I've skimmed through various posts on here and it seems to come up as a suggested option from various people. I'd considered whether to ask for slate or something but it feels like that would just do the same thing.
- ensure that the joists are set slightly away from the walls and don't touch them
I know that subfloor insulation is a divisive topic, and it is making me a little bit edgy. It was mainly a case of, if all the floorboards get lifted to remove the waste then I may as well do this too. Because the joists are being replaced, the floor now becomes a building control thing (they were already having to inspect some work elsewhere in the house) and therefore I'm not sure if I could get away with just not insulating at this point. I haven't actually been on site to speak to the BCO when they've been there in order to have a conversation along the lines of "i'm a bit worried about whether the damp has been resolved and would prefer not to install the insulation right now". This is to be determined.
