First floor scaffolding

[flanagaj]

I have the scaffolding company coming around this week.  The brickies have told me to get the first floor joists in and chipboard flooring and they'll use trestles.  This approach is great as I save money on having bird cage scaffolding, but given we are using 15kg medium density blocks internally, I'm concerned about the amount of weight when they load out the blocks.  They said they will put acro props under the floor joists, but I'm concerned it's not a great idea.  What have others done?

Edited September 21 by flanagaj

[Mike]

You seem not to have a roof yet? I wouldn't be installing chipboard anyway in that case, so I'd would stick with the birdcage (or I'd be using beam and block at 1st floor level).

[ToughButterCup]

10 hours ago, flanagaj said:

...  The brickies have told me to get the first floor joists in and chipboard flooring and they'll ...

 

They would tell you to do that. In addition to the quip about weight and blocks, the next thing they'll say is  "Oh, don't worry about the rain and the chipboard - it'll be fine. "

 

Birdcage - keep going

[Nickfromwales]

P5 Egger Protect is fine outdoors, as long as you are ‘weathered in’ in <90 days.

 

You can control the weight by asking that only x number of blocks are landed in any 1m2, or prop from underneath.

 

However, given the grief to date I think a birdcage is the best solution here; you may not appreciate the condition of the new deck after the brickies have been on it for the duration.

 

Birdcage isn’t expensive and they shouldn't need it for that long.

[dpmiller]

^ wot he said. The coated board is amazing stuff, ours was exposed for quite some  time with no ill effects. But if you can get scaff up handily, I'd do it...

[saveasteading]

16 minutes ago, Nickfromwales said:

Birdcage isn’t expensive 

Get several quotes. Some scaffolders have lots of kit and the timescale is secondary. Others have very little and effectively hire it to you. If you will need it to be adapted during the period, discuss that too. It's amazing how quickly they can do what they do when it is "included".

[flanagaj]

Was wondering what the logistics are in relation to installing the first floor posi joists.  They are obviously built in, so I assume they are fitted and then the scaffolders erect the bird cage?

[Mr Punter]

In the past I have put in temporary floor decks with 18mm T&G OSB which was later binned and replaced.  This was with treated timber joists.  As it was a 3 storey building and a bit fiddly there was no chance of getting up and in the dry quick enough.

[flanagaj]

On 22/09/2026 at 15:43, Mr Punter said:

In the past I have put in temporary floor decks with 18mm T&G OSB which was later binned and replaced.  This was with treated timber joists.  As it was a 3 storey building and a bit fiddly there was no chance of getting up and in the dry quick enough.

I didn't go with a bird cage as the scaffolding company we had chosen, didn't seem interested and never bothered to quote.  Posi joists have now been fitted and it's now raining.  Forecast for the next two weeks is bad and I won't get time to fit the chipboard flooring.  I have a pallet of OSB3 (ordered too soon) for sheething the roof so thinking I'll simply use that.  It's not T&G, but our posi joists are 95mm wide and 400mm centres, so actual span is small.  I just don't want to be responsible for someone accidentally going through the floor.   It's not ideal that the posi joists are exposed to the elements 😥

[saveasteading]

1 hour ago, flanagaj said:

going through the floor

The joists will survive but be surface affected ( look stained). Osb falls apart when wet so must be protected. Dpm will protect it but is slippy, and the water  will get through some places.

[Mr Punter]

The OSB will last at least 6 months before it is unsafe to walk on.  Don't put too many screws in.  When you are getting rid of it, someone will be happy to take it to reuse.

[saveasteading]

1 minute ago, Mr Punter said:

OSB will last at least 6 months before it is unsafe to walk on. 

I'm not convinced. Maybe it depends on the manufacturer, but where we have used it outside to protect other materials, and polythene has blown off, it fails rather worryingly.

[flanagaj]

2 hours ago, saveasteading said:

The joists will survive 

Will they straighten out.  Never seen such **** ever.  

[Gone West]

4 hours ago, saveasteading said:

Osb falls apart when wet so must be protected.

Depends on the grade of OSB. I've left bits of Sterlingboard OSB3 outside and only the edges have swollen.

[torre]

Our posijoists were similarly left open to the elements. We rolled offcut strips of DPM over the tops of them for protection before putting down an OSB deck and it kept them nice and dry. I was pleasantly surprised how well the OSB held up over a winter. Put enough screws in to protect against uplift as high winds can turn an 8x4 into a deadly kite, we used round head screws so they were easier to locate later after months of spills

[saveasteading]

7 hours ago, flanagaj said:

Will they straighten out.

If they are built with noggins then they shouldn't warp too much . But I'd very strongly recommend using treated timber. The extra cost isn't great. In the exposed situation it should dry as quickly as it wets.

 

I had a look at some of our old gash osb, where lying around or thrown on the wood pile. Most of it had been used as window opening covers. It is severely weakened and swollen. Of no use for anything.

 

You can get flooring chipboard with a temporary film precisely for this purpose (and to catch plaster and paint).   

@Gone West,  @torreand I can all be right, with differing circumstances.