I built my two storey extension for 20% of builder's quotes

This site shows how - step by step from design to completion

Installing First Floor Joists & Floor

Having fitted the sills, I headed up to complete the first lift. 

If you read my my earlier pages you will know that I was considering installing easi-joists at first floor level because I liked the idea of being able to easily run all my pipework. However, I knew the smallest available easi-joist is 195mm deep, and the joists in my existing house are only 150mm. If I used the easi-joist it would mean creating a small step on the first floor (I couldn't reduce the ceiling height downstairs as the ceilings are already very low).

Unsure if this was a good solution or not, I designed the depth of the extension so that a solid 150mm x 75mm joist would also be acceptable. 

I had my structural engineer do the necessary calculations and as I was close to the span limit for 150 x 75 joist I had to specify the higher grade C24 timber and also fit them at 400mm centres. (I have a copy of the floor joist span tables that still work but are no longer published in the Regs - let me know if you need any info)


more_bricksI eventually decided I could hide my plumbing fairly well without the easi-joist, and didn't really want the step, so went for the solid joist option.

Working from trestles (I got four from ebay for £30) and employing the old wall plate as my plank, I continued to build up the outer brick wall first.

I moved the builder's profiles having left some perps clear as before.




more_blocksFitting the insulation batts and wall ties as I went, I followed on up with the inner blocks.

I was going to use a mix of catnic style and also pre-stressed concrete lintels so I could achieve the effect I wanted (more on this later).

So I could match existing floor heights of the main house, I laid the lintels onto the wall as I got close to the right height.




dry_lintelsThen it was out with the trusty laser level again.

To take the floor joists, I was going to bolt a timber to the rear of the existing house. this is commonly done and I felt was easier than cutting brickwork out for every joist.

Form this timber, at 400mm centres, I would fix joist hangers. I chose to nail on the hangers in advance. The arms of the hangers were quite long so instead of cutting them off I bent them over the back of the timber and nailed them in for extra security.



timber_joist_hangersAt 500mm staggered height centres I drilled holes in the timber to accept the threaded bar that would bolt the timber to the wall.

I knocked a couple of bricks out of the back wall of the house at first floor level (where ultimately the doorway would be) so that I could match the floor heights.

As I was working alone, I rigged up some props to hold my timbers in place against the wall and marked where to drill the holes for my threaded bar. Each timber with its fitted hangers was around 4.5 Meters long, so it was a  bit of a handful, but I got there. 

I think I was a bit pre-occupied so forgot to take pics of the Heath Robinson propping arrangement. 

I needed to take down and repair a section of loose bricks above the door so I had something firm into which to set the bolts.   













first_joistI planned to fix the timber to the wall with 12mm threaded bar. The bar would be fixed into the brickwork with resin. A 14mm hole is drilled into the brickwork and half (ish) filled with resin. When the threaded bar is slowly twisted in, the resin squeezes out and around the bar to hold it in place.

There seemed to be many resins on the market, some in glass capsules and some in self mixing tubes. Of the self mixing tube type, some required a special gun, but some could be used in conjunction with a standard mastic type gun. As this would most likely be a one off for me I wanted to use a tube that fitted my gun.

I contacted Fischer and was advised to use their styrene free FPS30. The tech guy also advised me to get myself a small bottle brush to clean out the holes as neither blowing nor vacuuming does a very good job of removing all loose dust. 

He was right, the 70p brush was a great investment. It removed lots of dust and gave me the confidence that the holes were clean and ready for the resin.I could now support a joist in one of the hangers and, using a level, prop the other end to work out final blockwork height on the opposite wall.

first_joist2After much debate I chose to also fit joist hangers onto the wall. My other option being to rest the timber onto the blockwork.

My reasons were two fold. many councils now frown upon building onto block walls. This is because timber will shrink slightly as they dry out in the building and the slight gap that forms around the joist prevents it from being air tight. My Council allows timbers onto walls but insists on mastic sealer around the joist.

My other reason for using hangers was that technically it reduces the open span of the joist. 

joist_hangerNHBC guidelines advise that the joists or joist hangers should always be fitted onto whole blocks (though I have seen many cases where builders don't bother). Anyway, having worked out the necessary final block height I cut the necessary coursing blocks (the thin ones) and laid them first. The joist hangers should then be at the right height but on full blocks. Over the concrete lintels I had no choice but to use half depth blocks.

It was then just a question of cutting and fitting each joist. There should be a maximum gap of 6mm at the end of any joist, but as woodwork is an area I am comfortable with, I was happy I could cut and fit the joists accurately.  












restraintThe regulations suggested restraint straps to be fitted every 2 meters but I fitted more.

I only had two layers of blocks above the hangers but the mortar was well set and I was nice and gentle, but I went ahead and laid my flooring. I got chipboard flooring with a plastic coating to protect if from the weather. I then taped up the joints. I cut a hole in the corner and ran a 110mm waste pipe into the drain below in the concrete slab. I could then sweep any water away into the drains.



first_lift_blocksThe recommendation is that three layers of block are laid above the hangers before the floor is loaded. Working from a step ladder, I managed to build up two layers of block above the joist hangers before the weather turned. 

The taped joints of my flooring would have sufficed if it wasn't for the fact that I would be slow to get the roof on and the weather wasn't so damn ghastly. I hated water dripping through when it rained so I laid a sheet of DPM over the flooring.

Then December hit and in came the snow and freezing temperatures. I got no further construction done in December at all.

Early January I called in the BCO to check my first lift. He was happy with my work, but noting that the joists were close to maximum span, suggested I may consider doubling up the joists where a stud wall would be above.