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Extension floor thoughts.

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I have been working on the prep works for the extension over the past few weekends, yesterday saw the biggest development in edging me closer to the construction stage.


Basically I have an existing sunroom which will form part of the extension, to prepare the area for the build I had to demolish the inner block-work to enable to me re-jig things ready for the build.


Long story short I am now down to DPM on the inner wall which equates to about 220mm below floor level - what I have now is a room with a suspended timber floor with a 200mm gap around the perimeter, 100mm cavity and 100mm was the block - see here:






Let's try not to pay too much attention to the soaking poor blockwork, the rotten timber that is soaked from the door threshold not being correctly constructed and water pouring down the blocks etc.


So from this you can see where we are, the bottom photo is showing the long side of the sunroom and you can see the joists run long span across it and out of frame is a knee wall which supports the floor joists half way. So I need to get this all ready for a timber frame, so I started thinking last night and I have come up with some ideas.


So a brief description of where we are right now: We have on the short sides of the sunroom a 215mm wide wall up to DPC, (i.e. block built 215mm face down)100mm of the joists bearing on this, a knee wall in the middle, also 215mm wide, joists full bearing on this, and then as per the bottom photo, a joist runs parallel to the block wall.


I need to build a 5x2 timber frame kit onto this, leaving a 50mm cavity between timber frame and blockwork. Here are my options:


Option 1: 

Lift the floor (I need to lift some of it anyway to get under and do plumbing) and lay longer joists so that they extend to within 50mm of the block wall, that leaves me my 50mm cavity to the end walls and then on the long wall where the joists run parallel simply nail blocking out sitting on the the wall and nail a joist to the end of these spaced 50mm from the block wall, I can use some brackets to make sure it is solid as the full joist will be hanging over the wall held only by the blocking, however, the timer kit will partially bear on the blocking which is bearing on a wall, so I see no issue. I can then run 5x2 round the perimeter of the room to act as my sill plate for the timber kit to be built upon.


There are already battens attached to the bottom inside edges of the joists with 50/60mm Celotex in-between them, so with the floor deck off I can clip UFH pipes to this and biscuit screed the floor to top of joist, then lay whatever I need to lay on top of this to take a tile or maybe hardwood floor, ply/OSB over joists, or just normal 18mm caber?


This gets me to where I need to be, ready to build a timber frame!


Option 2:

Leave the floor as it is more or less (still need to lift some of it to do plumbing) and attach a 6x2 to the top of all the walls, so about 100mm would bear on top of the wall on the DPC and about 50mm would overhang the wall into the cavity reducing my cavity to 50mm, then I can nail a 5x2 on as a perimeter piece but step it in 11mm so the OSB sheet can go on top and leave my 50mm cavity. So the timer kit is basically built off the wall. I can then do my UFH within the joists as described above.


Option 3:

Remove the whole floor, reduce the height of the inner walls by a block or 2 and put in a beam and block floor, Robslee have done a design for me, I can sit the beams out to within 50mm of the wall for my cavity, the blocks would rest on a pad at the long wall wedge so I basically end up with a block and beam floor 50mm from the outer walls all all the way round and hard up against the existing house wall with a little piece of insulation. I then would lay blocks on there side to form a 215mm sill round the 3 external walls, put down 50mm insulation, UFH pipes and a 60-75mm screed. The blocks around the external walls would just be to contain the screed, I could then attach a 5x2 sill plate to the block and I could even bring the screed up to the top of the sill plate (I would also use insulation to insulate the block to stop cold bridging. 


All these options would work, I do like option 1 and 3 the best but I had not really budgeted for option 3, option 1 and 2 only really require some more lengths of 6x2 for joists (which I have in the garage I think) and I could probably have the floor sorted ready for the kit by Saturday night (not including the UFH stuff) which lets me start getting the sill plate down and get some "site" measurements for my timber kit. 


The downside to option 3 is the weight, looking at the spec from Robslee and working out roughly what the screed would way I reckon it's another 4 tonnes minimum - OK this is spread across the 3 short walls and one whole edge of the floor would be spread the length of the long wall I am just being cautious. 


There is possibly another option - 


Option 4:

The suspended floor has, from what I can see so far and measure a 650mm void below it - there is concrete over site on a DPM. Do I take all the blocks I have from the wall demo, and place them into the void, backfill with hardcore and sand and then DPM it again, insulate it all and pour concrete over site again but this time up to floor level? From the garage build and the demo works I reckon I have enough block and rubble and hardcore left over.


Also bear in mind that whatever I choose I really want to be rolling with these works again at the weekend so I need to bottom out details ASAP. I also have a baby due in 6 weeks so speed is a major factor here.


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Been thinking a lot about this today, to the extent I have hardly done any work!


I am tempted to go for one of the timber options - question is... which one. My thinking is if I go for option 2 but I wonder if this is seen as a bit of a bodge, albeit it I could construct it very carefully and make sure it's sturdy.



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