Extension floor

The main extension at the rear will have a suspended timber floor. This page will detail the steps taken to install it.

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On the 'walls to DPC' page you'll recall the joist hangers fixed into the new wall. There obviously needs to be a corresponding set on the opposite wall and these have now been fitted into slots cut into that wall. These will be mortared in the next time I start the cement mixer up.

The holes in the middle are where I cannot use hangers as there is a doorway, these will be made larger once I replace the tool I was using to cut out the bricks, which broke half way through the job.

One of the site foremen is seen here carrying out an inspection.

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At the far end there is the same problem in that I cannot use the joist hangers with no brickwork above them. There will be a doorway here also so I'll need to just sit the joists on top of the wall.

Here is the large hole I cut into the wall to allow for the joists. There is also the matter of the two drain pipes under the doorway here so I'll need to add a lintel across the top of those and that has meant a larger hole is required to cope with installing that as well.

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This picture of the opening for the new doorway where the old toilet was gives an idea of the differing floor levels.

The brick wall closest to the camera is at the level where the joists will sit on top of it. The far side shows how much will need to be dug out inside the existing house to get the timber floor in. Remember that there will also need to be a void under this of around 200mm. The oversite is already at that level on this side of the wall, it is just the demolition rubble that is piled up back up to the joist level and that will be removed soon.

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This picture shows the completed area of wall over the two drain pipes.

The lintel is in place (sitting on a DPC) and the wall above has been replaced, with joist hangers inserted to take the extension floor.

The wall above the opening will be removed to make another doorway into the existing house at a later stage.

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In order to provide the ventilation across the house I needed to place vents through the wall to link the under floor voids in the new extension with the one which will be under the existing house.

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Whilst the bricklayers were here they also built the dwarf wall across the extension in order to take the middle of the joist spans.

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Because the joists will be below the level of the damp proof course I need to protect the ends of them to avoid the possibility of them getting damp from the wall.

I could have wrapped the ends in the DPC plastic, but I decided that I would run a length of 300mm deep DPC roll around the perimeter of the floor and tuck it behind the joist hangers.

This will also stop the insulation touching what could be a damp wall.

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Where there are no joist hangers I also need to make sure the joists are not in contact with damp blockwork.

Here is the detail under the french doors. The vertical DPC has been carried across and an additional piece laid horizontally where the joists will sit (overlapped, of course). I have also added a thrid piece which tucks under the top of the vertical run and also the DPC across the bottom of the doorway.

I don't think I will suffer from rotting joists now.

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This picture shows all the joists having been put in place. They were all levelled by packing under the joist hangers where required so that they were all aligned with each other.

Noggins have been inserted at the ends where they are not in hangers to space them and prevent twisting. There are also some where one of the walls will be located as this falls between two joists and so needed support and fixing points to be in place.

The herringbone straps probably weren't strictly required as the joists are screwed to the wall plate on the dwarf wall and the floor boards will retain the top, but more is better to stop the joists moving.

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Where the openings will be I made holes into the inner leaf of the cavity wall so the floor goes all the way through.

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And this is the opening at the end of the room.

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Having finished the carpentry I started laying in the insulation.

This is laid onto netting draped over and stapled to the joists.

After the first few went in they were sagging in the middle even though I'd got the netting fairly tight. To deal with this I fixed two battens to the bottom of the joists to help the net support the insulation.

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And here is the floor with added fluffy stuff.

I've left two sections not done as I still need access there to move the water feed pipe.

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Having moved the water pipe I could put the vapour barrier down on top of the insulation and start placing the OSB flooring boards.

Here I'm half way through and you can see the vapour barrier on the left hand side of the floor.

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The floor was fairly simple, the pain was having to cut and fit noggins to support the edge of each board.

The only real problem came at the doors. Where the floor joists were levelled they were now slightly higher than the blockwork at the door openings.

This left the edge unsupported and would have cracked the tiles very quickly as the board flexed.

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I resolved this by adding a mortar bed on top of the blockwork that the vapour barrier and board would sit on.

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With the mortar in place I laid the vapour barrier over the top and gently laid the board onto it and pressed it down until it was sitting on the joists.

Once the mortar went hard it was supporting the edge of the boards and my tiles should now stay intact.

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Here's a shot of the completed floor.