Scaffolding tent for temporary roofing

[andyscotland]

So, following the latest instalment in the ongoing saga of my GRP roof I've been thinking more about trying to enclose it in a temporary tent so it can dry / I can break the increasingly depressing dependency on the weather. The BBC reckon it's now going to rain here most days for at least the next fortnight, and it is getting progressively colder and darker.

 

I'm aware there's loads of high-end temporary roof structure systems, but I'm not really up for getting a contractor / paying that kind of money. Just need to cover it for a fortnight or so so I can get this bit done then move on.

 

My thinking is a fairly basic scaffolding tube structure, with a sheet of clear polytunnel plastic stretched over the top / sides, stapled to / clamped between lengths of scrap timber around the bottom edges. I can get the polytunnel sheet big enough to cover the whole thing in a single piece, and good thermal / sunlight properties.

 

Here's a very rough mockup sketch of the idea. The garage is an L shape round the corner of the house, so one side of the structure would have to sail over the corner of our roof hip - probably with a bottom member resting on it on some foam / PIR offcuts to protect the slates.

 

The legs would be secured to the building, possibly with scaffolding eyes, short tube, clamps, or possibly with eyebolts and rope / ratchet straps (depending on what I can cobble together easily).

 

Have kept the outer legs to 3.9m to keep the wind-exposed faces smaller, would still have about 4 - 5 foot of head height inside the tent, enough to comfortably crawl about to work.

 

The idea would be to get the bottom edges of the sheeting close enough to the walls / house roof that between a fan heater and solar gain I could get the temperature up a wee bit above ambient to help the decking dry, and subsequently to be a bit warmer for the actual GRP process. Thinking once I have the structure weatherproof I can afford to leave it a week (or more) till the boards are all properly bone dry and then do the laminating / topcoat when it suits rather than having to try and grab a weather window and hope it doesn't unexpectedly bucket down as it has half way through the last two "good weather days".

 

Obviously scaffolding doesn't need to be loadbearing, tho don't want it to collapse under self-weight / any water that ponds on the sheeting (which it shouldn't do too badly if pulled tight). And equally obviously don't want it to blow away / covers to rip off in a storm and soak it all again. Have built quite a lot of basic scaff structures over the years, tho mostly indoors without need to worry about wind loading etc.

 

Questions:

• Has the weather and frustration driven me stark raving mad?
• Any thoughts on strength / stability?
• Have found a couple of local companies that will dry-hire scaffold tube & clamps but only with a trade account which is proving a hurdle - anyone know of a supplier that will hire to self-builders (in or able to deliver to Central Scotland)? It's not a massive order, reckon 30ish lengths of varying lengths of barrel and a couple of crates of clamps.
• Or would I be better buying the tube and then selling it on second hand? Have found a few companies selling used tube online for not much less than brand new - anyone got tips for a firm that would buy it back after, or am I going to be sat with it on the drive till I find a private buyer (which would probably drive SWMBO even more round the bend than the current lack of roofing progress)?

 

I know people here have had good results buying then selling e.g. Kwikstage, but that generally seems to be for longer periods - I will probably need it 3 weeks - a month at the outside - and from what I've found so far there's less of a market for traditional barrel. System scaffold I think less likely to work for me given the weird shape and some longer spans, but happy to be corrected.

 

[ProDave]

Making it stand up to the wind will be your biggest challenge.

 

The last few days have been "west coast" weather here for sure. It has barely stopped raining since Friday, most unusual for this side.

 

I have had the scaffold up to fit a velux window now for well over a month. I am almost resigned to the fact it is not happening this year.

[Visti]

The structure:

1. You've not got anything to bear the load across the structure from the top-left to the bottom-right. If you are going to do this,  use a triangular 
2. Your longest horizontal pole is about 5-6m? You'll want to use a truss or support that in the centre. I'd want to use trusses for all of the roof portion if I was you.
3. You need a decent fall from one side to the other, at least 10% if not more, for rain runoff.

The Idea:

1. Water will pool between your poles, even with a fall. That can lead to a lot of weight unless you stay on top of it. 
2. Water runoff looks like it'll strike your neighbour - suggest some plan to deal with that.

 

High note of caution from me who has done something similar; wind is frightening at that scale with a tarpaulin.

 

We spent £500 for a similar setup to cover 11x11m, and £250 for a 12x16m tarpaulin.

 

It did the trick, but you can see the setup was very heavy duty and even so the tarpaulin received a lot of damage in the process, with bungees snapping and the poles ripping into the wind driven tarp.

 

How a polytunnel will hold I don't know.

 

 

 

 

[andyscotland]

4 hours ago, ProDave said:

Making it stand up to the wind will be your biggest challenge.

 

Absolutely - that's the bit I'm nervous about really.

 

Quote

The last few days have been "west coast" weather here for sure. It has barely stopped raining since Friday, most unusual for this side.

 

I have had the scaffold up to fit a velux window now for well over a month. I am almost resigned to the fact it is not happening this year.

 

I don't think I can resign myself to not getting the roof finished this year : no chance the tarps currently on it will hold up that long, have essentially run out of anything useful indoors I can do till properly watertight and my mother in law is due to come and stay in it for a few weeks in Feb while she has her own building work done... ?

[andyscotland]

@Visti Hugely helpful, thanks.

 

* Longest horizontal pole around then edges would be the 4.5m span over the neighbour, which I'd thought of supporting with the diagonal bracing though realise a truss would be a lot better if I can source.

 

* Longest horizontal over the top is 4.8m and yes had been thinking that really would be pushing it without bracing/truss.

 

* On current idea the fall would be about 12 degrees, 20ish %

 

* Yes have been finding water pooling on the current tarps (which are only ~ a foot above the deck and supported on catenaries slung between a few timber blocks round the edges, had to get something up as a quick cover). Would expect to be up regularly pushing it out.

 

* The join isn't actually to neighbours house but to their box gutter installed over the gap between the two of us when they did their extension and (by agreement) fixed to our wall. So no issue with our rainwater dropping down into that short term, they're happy with that.

 

* Should clarify the area is sheltered immediately either side by the two houses (bit more than half a storey taller), less so front to back but the house over the road and trees at the bottom of our garden do seem to break the wind up a bit most of the time. Have had various combinations of breather membrane held down by timber / bricks just sitting

on deck and draped over rooflight upstands, tarps floating over the top through a mix of tying off to sides and a few ropes underneath etc for more than a month now including through some reasonable storms and although it's got a bit flappy sometimes (and done a fair bit of damage to the tarps, on second set now) it's not seemed at risk of actually ripping eyelets out / ropes off fixings. Appreciate raising it further above the roof and putting sides on will increase wind exposure.

 

I'm not entirely clear how polytunnel would hold up either, tho thinking a) it is designed to be stretched over a fairly open frame in a field for years so presumably fairly robust and b) if it was a bit weaker than tarp that wouldn't be a bad thing as would rather thin plastic ripped and flew away than the whole structure went with it if it got really wild?

 

Was your £500 for the trussing supply only or did that include labour? How long did you have it / did you find it easy enough to source?

 

 

 

[Ferdinand]

Would it be worth actually concreting in the posts which are going to get the "up" vertical wind load, using a block with the top slightly below ground so you can just saw it off and cover later? Would that be of any material benefit?

 

Depends on whether your wind direction is relatively constant (?)

 

Empahsize: I am not experienced at this, but I have seen a scaffs blow over.

 

[Visti]

£500 for the entire scaff setup you can see in the photos. Cash deal with labour to install and strike down 2 months later. They had us for the scaffold for the whole house, so I had some leverage of future business with them.

 

Key point of note was that we were warned not to tie the tarpaulin to the scaffold itself, but to weigh down the tarp as best we could independently. You can see we did what we could, but in some cases we did tie it to the scaff.

[Cpd]

Not sure if you have talked about securing it but I have found that the best way to secure tarps / plastic is to clamp the lower edges (screw batten to batten) between long lengths of timber and then screw / clamp  the timber into something solid, it’s best to roll the bottom of the plastic over itself so it does not pull out. I would also buy a large roll of cheep string, bailer twine is fine and create a web over and between the scaffolding on top to prevent pooling, you can add to this as required afterwards. Pooling water was always the biggest problem for us and even with a GOOD slope you would get problems at the lower end with water pooling behind the tension of the tarp or cross memberS, as soon as the water starts to pool it pulls all the spare tension out of the tarp into that one area creating a bigger pool, very quickly it becomes very heavy and without somewhere to go will put a lot of tension on the weakest link and something will give, if using greenhouse plastic it will split under these conditions as it’s just not designed to be load bearing, a good tarp would be stronger. Also green house plastic will damage much quicker and again will not stand up to being tensioned for long periods over anything sharp like a bolt head without splitting. I used to have to tarp our jobs in Australia to enable us to work power tools in the rain...... they always failed at some point if not constantly tweeted and maintained. I think your plan could work but it’s going to need to be very robust if it’s to be up for any length of time. 

[Russell griffiths]

Just going back to your last thread about your roof, something I did that I didn’t see you do was actually dry, warm the roof I read that you checked with a moisture meter but when I did mine I actually used a large blowtorch and heated the ply until I could see all the moisture steaming off it, I got it so it was so warm to touch it was too hot to put a hand on it. 

I did this all over very quickly, then went over it again before I made a mix, then laid on the resin whilst the boards where warm, did mine in January with 4-5 hour dry windows in the weather. 

[Visti]

Some great suggestions @Cpd, I wish I'd thought of that for ours!

[Ferdinand]

Is lorry curtain better than tarp?

[Vijay]

1 hour ago, Ferdinand said:

Is lorry curtain better than tarp?

They are flipping heavy!!!

[andyscotland]

Hey, thanks so much everyone for the excellent comments.

 

15 hours ago, Ferdinand said:

Would it be worth actually concreting in the posts which are going to get the "up" vertical wind load, using a block with the top slightly below ground so you can just saw it off and cover later? Would that be of any material benefit?

 

Depends on whether your wind direction is relatively constant (?)

 

Empahsize: I am not experienced at this, but I have seen a scaffs blow over.

 

 

Might work if I buy it, not sure how a hire company would feel about that ? tbh gut feeling is I'd be a bit nervous about relying only on friction to hold the tube in the concrete if there was significant upwards wind load, suppose could faff about drilling some bolts or similar through the tube before casting to give more of a mechanical interlock.

 

15 hours ago, Visti said:

Key point of note was that we were warned not to tie the tarpaulin to the scaffold itself, but to weigh down the tarp as best we could independently. You can see we did what we could, but in some cases we did tie it to the scaff.

 

Thinking this (coupled with @Cpd below clamping into battens and then fixing the battens into something solid) is a better idea. I already have a fair few tie-off points from the current tarps and know that they're holding up OK to the wind. So potentially would fix tarp/sheeting into battens, drill holes into the ends of the battens and tie them off to the building as now - and not actually worry too much about restraining the scaffolding itself - so if the wind gets extreme the sheeting might rip off and fly away but the structure itself would then be unlikely to go anywhere...

 

14 hours ago, Cpd said:

Not sure if you have talked about securing it but I have found that the best way to secure tarps / plastic is to clamp the lower edges (screw batten to batten) between long lengths of timber and then screw / clamp  the timber into something solid, it’s best to roll the bottom of the plastic over itself so it does not pull out. I would also buy a large roll of cheep string, bailer twine is fine and create a web over and between the scaffolding on top to prevent pooling, you can add to this as required afterwards. Pooling water was always the biggest problem for us and even with a GOOD slope you would get problems at the lower end with water pooling behind the tension of the tarp or cross memberS, as soon as the water starts to pool it pulls all the spare tension out of the tarp into that one area creating a bigger pool, very quickly it becomes very heavy and without somewhere to go will put a lot of tension on the weakest link and something will give, if using greenhouse plastic it will split under these conditions as it’s just not designed to be load bearing, a good tarp would be stronger. Also green house plastic will damage much quicker and again will not stand up to being tensioned for long periods over anything sharp like a bolt head without splitting. I used to have to tarp our jobs in Australia to enable us to work power tools in the rain...... they always failed at some point if not constantly tweeted and maintained. I think your plan could work but it’s going to need to be very robust if it’s to be up for any length of time. 

 

Brilliant tip on the twine, cheers. That's got me thinking potentially more tensioned rope/twine web and fewer horizontal members over the top (which I only really put there to support sheeting) - suspect I might get less deflection in a tight rope than from the self-weight of a long bit of scaff.

 

With a rope web to shape the sheeting, could also possibly think more creatively about roof shape - either a gable with a steeper fall, or a surface that acts more to funnel water down to one corner / low spot on the basis it'll be easier to prevent / avoid ponding in one small spot than along all the edges of the frame.

 

Was thinking perhaps KEE clamps rather than traditional scaff clamps around most of the top frame to minimise places the sheeting is stretched over bolts etc, and padding any unavoidable bolts with e.g. foam.

 

The more I think about it, the more I think it's likely to be up a fortnight at the most - day to build it, perhaps a week to be sure the decking has completely dried and then (as there'll be no need to work round weather and daylight) at most 2 days to do the GRP and topcoat.

 

But am thinking maybe I should still go tarp (which I have most of already) rather than clear plastic. Main reason for the plastic was to allow the sun to help heat it, and to have plenty of light for actually doing the GRP - but can solve both those other ways without too much cost.

 

13 hours ago, Russell griffiths said:

Just going back to your last thread about your roof, something I did that I didn’t see you do was actually dry, warm the roof I read that you checked with a moisture meter but when I did mine I actually used a large blowtorch and heated the ply until I could see all the moisture steaming off it, I got it so it was so warm to touch it was too hot to put a hand on it. 

I did this all over very quickly, then went over it again before I made a mix, then laid on the resin whilst the boards where warm, did mine in January with 4-5 hour dry windows in the weather. 

 

We did try drying - both slowly with fan heater under the tarp blowing over the boards, and rapidly with electric heat gun as we were preparing to work. Found the heat gun very slow going to get any sort of useful temperature, and I was a bit nervous of drying the surface but leaving moisture in the core. A blowtorch to the point of steaming would work better I'm sure, though would need to get one and would be a bit nervous of starting a fire. Also several of the damper areas are very close to the trims, and to some areas that are already bandaged : would be a bit nervous about how extreme heat would affect those?

 

I think where I'm at now, if I knew I'd have 4-5 hour dry windows that'd be fine (and maybe I should get over myself and JFDI) but as I've twice now had rain come suddenly out of nowhere despite perfect forecast, it's feeling like every time I attempt it it's a day off work to go one step forward and two back. Just takes so long getting covers off, getting covers back on robustly, etc.

 

[andyscotland]

 

14 hours ago, Ferdinand said:

Is lorry curtain better than tarp?

 

13 hours ago, Vijay said:

They are flipping heavy!!!

 

Yeah could cover pretty much anything with a lorry curtain I reckon, but a lot more engineering needed to support the curtain itself...

[JFDIY]

8 hours ago, andyscotland said:

I'd be a bit nervous about relying only on friction to hold the tube in the concrete if there was significant upwards wind load

 

You could put a scaffold clamp on the tube good and tight before casting the concrete around it.

[Ed Davies]

9 hours ago, andyscotland said:

but a lot more engineering needed to support the curtain itself...

 

I'd think that wind load would be more significant than the weight of whatever plausible material you might use.

 

Scaffold sheeting might be worth looking at. Mine, as shown in that blog post, failed but the initial failures were mostly due to the ropes I used to tie the sheets to the frame chaffing through on the corners of the timbers. Only when a few of those had failed and largish areas were flapping around did the scaffold sheeting itself start to rip. There do bungee-like cords with plastic bits on the ends to stitch the edges of that sheeting to scaffold poles - they'd probably do a lot better than ropes round squared-off timber.

[Ferdinand]

2 hours ago, JFDIY said:

 

You could put a scaffold clamp on the tube good and tight before casting the concrete around it.

 

We used a scaffold foot stood on a first pour, then added a clamp and filled up the hole iirc.

 

It was the anchor for a 6m tower for a 1m satellite dish.

Edited November 6, 2019 by Ferdinand

[Ferdinand]

11 hours ago, andyscotland said:

 

 

 

Yeah could cover pretty much anything with a lorry curtain I reckon, but a lot more engineering needed to support the curtain itself...

 

But will not rip.

[Conor]

My neighbour used a pop-up gazebo. You only need to cover the sections you are working on (for the rest of the roof, use flat tarps with 2x4s under to keep off the deck), and remember the chemicals cure reasonably quickly so you can move it as you work.

[andyscotland]

More brilliant tips, thanks folks.

 

4 hours ago, Ed Davies said:

I'd think that wind load would be more significant than the weight of whatever plausible material you might use.

 

True, was just thinking wind loading may be primarily horizontal / upwards where heavier sheeting combined with the self-weight of the scaff would mean more need to brace / support against downward load.

 

4 hours ago, Ed Davies said:

Scaffold sheeting might be worth looking at. Mine, as shown in that blog post, failed but the initial failures were mostly due to the ropes I used to tie the sheets to the frame chaffing through on the corners of the timbers. Only when a few of those had failed and largish areas were flapping around did the scaffold sheeting itself start to rip. There do bungee-like cords with plastic bits on the ends to stitch the edges of that sheeting to scaffold poles - they'd probably do a lot better than ropes round squared-off timber.

 

Very good thought, thanks. Immediate thought looking at your blog is I'd need to work out how to reliably support / lap / join the edges (or find it in more than a 2m width) but definitely looks a more robust option.

 

2 hours ago, Conor said:

My neighbour used a pop-up gazebo. You only need to cover the sections you are working on (for the rest of the roof, use flat tarps with 2x4s under to keep off the deck), and remember the chemicals cure reasonably quickly so you can move it as you work.

 

That's actually not a bad point. Maybe I need to separate out my thinking on "protecting & covering it to let it dry out" (which the current tarps are kinda doing) from "covering the area we're working on till it's safe to get wet". That said have found in the sections we've done so far that although the main resin has cured pretty fast it's still been tacky and developed very thin milky surface patches where dew / raindrops have landed on it several hours later. Fine at this stage as that comes off with a very light sand, but want to be pretty sure the topcoat will stay dry till it's totally cured. Don't really want to do the topcoat in lots of little sections either, presume that might show up a bit...

 

But definitely worth thinking about.

[Conor]

@andyscotland you definitely want to do the top coat as continuous coats. But it's the fastest and easiest part of the job. You'd have that area painted in less than two hours.

[Visti]

Can second the lorry curtain, it is heavy as f**k. I exhausted myself manouvering ours around. I've cut it up into 4 smaller sheets to be able to manhandle them better

[SteamyTea]

Or you could change to a polyurethane resin system that is moisture tolerant.

If you were not at the wrong end of the country, I would come and help, be fun to try out a new system.

 

https://www.apolloroofingsolutions.co.uk/product-overview/single-component-pu-waterproofing-system/

Edited November 7, 2019 by SteamyTea

[Onoff]

Just now, SteamyTea said:

polyurethane resin system

 

Tell me more, like paint is it?

[SteamyTea]

4 minutes ago, Onoff said:

Tell me more, like paint is it?

Never used it, or seen it in action.

But I have used PU resins a lot in the past.  They are tolerant of moisture, some actually need it to cure.

I seem to remember that they are more viscous, so may seem a bit alien to people that are used to polyester, and I am not sure how easily they break down the binder in the mat.

There are different types of binder for mat and woven cloth does not have any at all, so that may be an option.

Call them up and ask for a sample. 

You are on the wrong side of the country too.

 

Edited November 7, 2019 by SteamyTea