Intro: Wooden Scaffolding Tower
As part of building my new workshop it was necessary to first remove an old and poorly built extension (addition) to our house. After seeing how much a builder wanted to do the job that gravity was already doing for free I decided to tackle it myself.
Although the extension was only a single story and flat roofed it was awkward in just about every way you can imagine. Due to a major quirk with the construction the flat roof was anything up to 5m or 16' above ground level and there were actually two complete roofs - a pitched roof internally and a flat roof externally.
Normally an extension like this would be taken down largely from above by walking around on the roof taking it to bits and throwing it over the side as you work. That wasn't going to work here though because of how badly the roof timbers had failed. Any additional load (e.g. me) could have resulted in total collapse so I opted to very carefully take it down from inside which meant I needed a moveable tower type scaffold.
Heath and Safety Warning
Working at height is dangerous! The Health and Safety Executive statistics shown that nearly a quarter of workplace fatalities are caused by falls from height. If you don’t feel you can complete a project like this safely don’t even start. Home made scaffolding is right up there with home made rocket cars in the danger stakes.
If you want even more detail...
I've tried to cram everything you need to know to complete this build into this instructable but it's a big build with a lot of things to consider. If you want even more detail the full write-up on Wobblycogs Workshop (my main site) runs to over fifteen thousand words.
Before I decided to build my own scaffolding tower I did some research into towers that you can buy. I love building things but I decided that if I could buy a decent tower for less than I could build one then I'd do that. Towers are very broadly split into three options:
- Old slot together steel pipe designs. These can be picked up for next to nothing but are an accident waiting to happen.
- DIY class tower that are good for things like painting upstairs windows / cleaning guttering / etc.
- Trade quality towers that are good for light to medium construction.
As you can probably imagine the price goes up with quality. DIY towers are good for what they are designed for but they aren't sturdy or stable enough for building work. Trade quality towers with a working height of 3.7m typically start around £700 new. Bargains can be picked up second hand, normally on taller towers, but then you have the problem of transporting it and getting spares.
Step 1: Design
Before starting any large build I like get at least a rough design put together so I know I'm heading in the right direction. As safety was a primary concern for this build I went to town and produced a detailed design to make sure everything would work together.
That's not to say that everything I designed worked perfectly. There were a few modifications as the build progressed mainly caused by the fact the final structure was quite a bit heavier than I had expected. The screenshots shown here are the final design with all modifications included.
I also put together a set of drawings which are linked below. The drawings show enough detail to build the scaffold, they are what I worked from, but they do require you to think about what you are doing.
Step 2: Calculations
Just looking at the design I was fairly sure that what I intended to build would be strong enough but I wanted to see some figures backing that thought up. The platform was my main concern as this was the first time I'd every built a structure that spanned a reasonable opening.
The working platform is built like a floor in a house and so it seems reasonable that the calculations and tables used for floors would also work for my platform. I have more detail on my main site but to summarize the calculations worked out like this:
Going by the BS6399-1 building regulations (superseded but I could find figures from this version) a wooden floor should be designed to support 153kg per square meter. My aim was to make the platform at least this strong.
The platform would be built from C16 dry graded lumber with a dimension of 47x97mm (approximately 2x4") with 450mm centres (approx 18"). These are standard construction dimensions and so the maximum span can be looked up in a table. For these dimensions the maximum span is 1.82m (approx 6').
My platform had the following dimensions:
- Width: 840mm
- Length: 1800mm
- Joists: 47×100 C16 on 450mm centres
- Span: 1500mm
The surface area of the platform is 1.5m^2 which gives a maximum safe working load of 1.5*153=230kg assuming it's built to the regulations. Since my designed span is significantly less than 1.82m I was more than happy that it was strong enough. On top of that the average joist spacing is quite a bit less than 450mm, the deck is 18mm hardwood ply rather than chipboard and my supplier sent me C24 timber rather than C16. I would guess the safe working load is actually somewhere over 300kg.
Step 3: Tools and Materials
As I had to make up a single large order for the timber I have a good record of what I used. The hardware list is certainly close but I might have missed the odd bolt or washer - I buy hardware like nuts and bolts in large packs as it's cheaper so I don't tend to count everyone I use.
These are the parts I used in the construction. A couple of parts are optional because I either didn't fit that part or I found a better way of solving the problem. Measurements are in millimetres.
- 4 * Kickboard Long Support 50x50x100 - optional
- 2 * Long Rail Stiffener 50x50x1700
- 2 * Platform Stop 50x50x840 - optional, a better method was designed
- 4 * Rail Support Block Small 50x50x100
- 4 * Rail Upright 50x50x1200
- 4 * Cross Brace 47x100x2400
- 4 * Noggin (Short) 47x100x126
- 3 * Noggin (Long) 47x100x400
- 4 * Platform Joist 47x100x1800
- 2 * Rail Support Full 47x100x846
- 16 * Rung 47x100x940
- 4 * Leg 47x150x2340
- 4 * Stretcher 47x150x1800
- 2 * Rail Long Stretcher 25x101x1800
- 2 * Rail Long Mid Stretcher 25x200x1800
For the parts above you'll need to purchase the following timber. This timber should be readily available at any building material suppliers and large DIY stores. Cross sections are in millimetres (e.g 50mmx50mm), lengths are in meters.
- 50x50mm @ 20m = £25.20
- 47x100 @ 40 = £84.48
- 47x150 @ 20 = £63.36
- 25x100 @ 4 = £6.24
- 25x200 @ 4 = £12.96
All parts can be cut from a single sheet of 18mm hardwood ply mine cost £33.12.
- 1 * Platform Bed 18x840x1800
- 2 * Cross Brace Gusset 18x225x240
- 1 * Hatch Bed 18x440x440 - can be cut from the bed with care
- 2 * Kickboard Long 18x150x1600 - optional
- 2 * Kickboard Short 18x195x840 - optional
- 2 * Rail Short Stretcher 18x100x840
- 4 * Rail Support Plate 18x100x151
All measurements are in millimetres.
- 32 * M10 x100 Bolts
- 64 * M10 Washers, use thick repair washers
- 24 * M10 Nylock Nuts
- 8 * M10 Wing Nuts
- 20 * M6 x 70 Bolts
- 32 * M6 Washers
- 20 * M6 Wing Nuts
- 16 * M5 x 50 Bolts
- 16 * M5 Washers
- 16 * M5 Nylock Nuts
- 30 * 4 x 50 Wood Screws
- 64 * 4.5 x 70 Wood Screws
- 32 * 6 x 150 Wood Screws
- 1 * Exterior Wood Glue 1000 ml
- 4 * Heavy Duty Castor, 60kg or greater
- 1 * Bottle Jack 1 Ton or greater
I didn't keep track of tools that I used during the build but I didn't use anything you wouldn't find in a woodworkers workshop. A powerful router with a long straight cutting bit is a must and a jigsaw came in handy. Other than that it was just regular woodworking tools. The only slightly exotic tools was a pillar drill which was used to ensure holes in the guard rail were perpendicular to the face, this could be done with a hand drill with some care.
Step 4: Building the Long Sides
Cut the Legs and Stretchers to Length
The legs and stretchers are the most import part of this build as everything depends on all four of them being identical. I’ve used 47x150mm (2″x6″) timber for the legs and stretchers.
Square off one end of each piece of timber and then measure and mark them all at the correct length. Lay the pieces side by side to help prevent mistakes. Once you are happy they are all marked up correctly cut each piece. Normally when I need multiple pieces all exactly the same length I will gang cut them (e.g. cut all the pieces at the same time) but the legs in particular were proving difficult to get on the saw more than one at a time.
Some Simple Jigs
The whole scaffold is bolted together and it’s important to make sure that the holes through which the bolts will run are perpendicular to the face of the timber. Also, the holes should also be a snug fit for the bolt so that you have to lightly tap the bolt through.
For regular sized pieces of timber the easiest way to get a hole square to the face is to stick it on the drill press but clearly this wasn’t going to work here. My solution was to find a scrap of wood and drill a 10mm hole in it on the drill press and use that as a drill guide for the scaffolding. To locate the drill bit at the start simply counter sink where you want to drill. The countersink bit will give a good indentation that the drill bit will naturally fall into.
The other jig that is invaluable is a guide for the Forstner bit used to counterbore for the washers and bolt heads. This is simply a piece of thin scrap material with the appropriate sized hole drilled in it. I drilled two different sized holes as the smaller one was only just large enough for the washers I was using. When you want a counterbore place the jig on the timber, press down firmly and insert the Forstner bit. Once the Forstner bit is sunk a couple of millimetres into the work piece the jig can be removed to aid chip removal.
Prepare the Stretchers
Mark up the stretchers as per the plan and drill through them. The holes should be 75mm in from the end and 35mm in from the edge. The level of accuracy you’ll be able to achieve won’t be good enough that the pieces will be interchangeable so exact hole placement isn’t vitally important.
Cut the Rung Sockets
Each leg has eight rungs that are let into sockets cut into the leg. Start by laying all the legs on their side and carefully aligning what will be the bottom / foot end. Use a mallet to tap on any legs sticking out proud to bring all the pieces into perfect alignment. Using a square and a ruler mark the location of the rung sockets. It’s important that you always measure from the bottom of the leg every time.
Use a jigsaw to cut a couple of millimetres inside the layout for the socket and then chisel out the scrap with an old screwdriver. With the sockets roughly cut out gang up the leg pieces again using the rung marks for alignment. Make a guide bush routing jig for cutting the sockets and route the first rung socket. The jig is simply two parallel pieces of timber spaced the width of the rail plus a little for the bushing. I say a little because it depends on the router bit and bushing combination you are using.
Assuming your jig is set up correctly you should now be able to slide a rail down into the first set of sockets. Leave this first rail in place while you rout the other sockets as it will ensure that legs are held firmly in alignment. If necessary at the end trim the bottom of the legs flush. This will create paired legs
Step 5: Completing the Long Sides
Attach the Stretchers
Lay two legs down, propping them up on some scraps to make clamping easier, and then lay the stretchers on top. Make sure that the rung sockets face in since this is the final arrangement of the scaffold. Using a large framing square clamped to one of the legs square up the stretcher relative to the leg. I found using a piece of box section steel also help but it’s not entirely necessary.
Once you are happy that the stretcher is square at one end drill through the stretcher and the leg and then insert bolts to hold the completed corner square. Congratulations, the most difficult part is now complete. Repeat the process for the remaining three corners and then take it all apart and turn it over.
Using the Forstner jig made earlier counterbore each bolt hole in the leg. Push bolts back through the holes this time making sure to include washers. Using a spanner and a socket wrench tighten up the bolts.
Once all four corners are bolted tight measure the corner to corner or distance of each diagonal. If the frame is out of square it will show as a difference in the two measurements and you need to tap on the longer diagonal with a mallet until the measurement is the same as the smaller diagonal. In my case the difference was just 2mm which is great on a frame of this size.
Attach the Cross Bracing
The cross bracing that will be fitted next goes on the outside fact of the leg which means the frame needs to be carefully turned over. It’s worth measuring it for square after it’s been moved but it should be able to handle this level of movement.
Lay a piece of bracing timber diagonally on the legs, mark where it overhangs the leg and cut it off with the jigsaw. I used a couple of scraps to keep the bracing away from the stretchers but this was just for looks. As long as your bracing runs roughly from corner to corner it doesn’t matter exactly where it goes.
Layout for a bolt to hold the bracing in place and then drill it at 10mm diameter both ends. Remove the first piece of bracing and then repeat the process for the other diagonal. It's now necessary to cut a half lap joint in the middle of both bracing pieces.
Fit one brace and then lay the other over the top and using a couple of extra long 10mm bolts pin the top piece into place. It’s then a simple matter of marking exactly where the two pieces need to be socketed. Routing out the socket for the joint can be done using the same jig as was using for the rungs. Note that the jig will have to secured at an awkward angle in order to cut this joint. Rather than try to customize the jig I simply nailed it to the bracing.
Lay the two pieces of bracing on the legs and fit them together. I found I had a slight bow in one piece of bracing stock so it tool a little persuasion to go home. Once it was home I secured the joint with a screw. As with the bolt holes for the stretchers the bolt heads will need counterboring for the bracing. This can be done one at a time once the piece is turned over again.
Step 6: Assembling the Tower
Start by putting the two long sides up against each other orientated as they would be in the final product. Check to see how accurately they match each other. In my case I had about 3mm of error over the 2.1mm length. A quick bit of calculation shows that the error is less than 0.1 degrees, pretty good I think.
Dry fit a couple of rungs so that the scaffold can stand on it’s own. I did this on my own but I would highly recommend getting a friend to help as it was a bit touch and go as to whether it would all fall on me. The problem is simply getting the two sides to both stand perfectly vertical while you hammer home a rung.
The technique that worked for me was adding two rungs to one long side which it was leaning against a wall then offering up the other side. With some care I was able to stand the first side up while hammering the top run home. Once that first rung was home the scaffold was quite happy to stand on it’s own which made like much simpler. I then dry fitted rungs top and bottom on the other end to give the scaffold a little more stiffness.
Once I was happy the structure was safe and square I glued and screwed one rung at a time into place.
Now add some corner bracing at the base of the tower. As usual I went to town and used some off cuts of 50×150 for the bracing. The reason for using such large corner bracing will become clear later but each piece was fitted with four 6x150mm long screws.
With bracing fitted in all four corners and the top and bottom rungs in place it was then just a matter of fitting the other rungs. It took about an hour per-end to glue and screw all the rungs into place.
Step 7: Building the Platform
With the tower basically complete it's time to build the platform. Lay a full sheet of 18mm hardwood ply on the floor and using a track saw cut the long edge of the platform. Move the supports under the ply and cut the platform to length. At this point it will probably look a bit small but trust me it’s more than large enough.
Cut the four beams that will support the platform to length. Optionally slide everything into the tower and test it out, this really isn't necessary but I couldn't resist.
Mark the locations of the noggins on the centre beams. Clamp everything together and drill and screw the noggins into place using 5x120mm or 5×100mm screws. Make sure you accurately position the middle noggin as that defines your hatch opening.
Place the platform sheet on the workbench and clamp down the outer beams. Cut noggins to fit the gaps and secure the outer beams to the centre beams.
Mark the location of the hatch by tracing around the opening. Measure out about 15mm from the marks and draw a new hatch opening. Drill holes at each corner and use a jigsaw with a fine blade to cut the hatch free. A circular saw with a plunge feature could also be used.
Take the sheet off the workbench and put the frame back then lay the sheet back down on top. Evenly space holes about every 250mm down the sheet and drill and screw it to the frame, 4.5×50mm screws work well.
The platform is now complete. With help from an assistant slide the platform into place. Take care at this stage, the platform has to be slid straight into the scaffold. If there is any misalignment it’ll jam and things can rapidly start to go wrong.
With the platform is in place it would be criminal not to have a climb. The platform moved slightly as I climbed it highlighting the need for some fixing mechanism. It was safe enough that I lounged around a bit though.
Step 8: Moving the Scaffold
My scaffolding tower was a bit too heavy to move by just dragging around so I needed some sort of dolly system to move it. The solution I came up with was simple and incredibly effective.
I decided on placing the castors on a frame that fitted inside the legs of the scaffold and push up on the corner bracing. The first thing I needed to do was cut my dolly frame timber to length and then join it together. By necessity the joints would be right where the castor wheels would be so they needed to be strong and I settled on half lap joints. For speed reasons I decided to trench cut each end of the joint on the mitre saw first.
The short edges were made from 50×150 mm offcuts that I had left over from the legs. The long edges were made from 50×100 mm rung left overs. The mortice in the long edges had to be inset from the end by about 50mm in order for the castor to line up correctly with the centre of the beam and still be able to rotate within the scaffolding tower.
Once the trench cuts were complete and the mortices defined I cleaned up the rest of the mortice with the router.
Once all the joints were cut I did a quick test fit of the dolly frame. Rather than put it under the supports which would be awkward I put it together on top of them. With everything fitting nicely I took the dolly frame out, put it back together and laid out for the castors. After a lot of drilling and counterboring I bolted on the casters. The tops of the bolts holding the castors have to be sunk beneath the top of the dolly frame as this is the face that pushes up on the corner bracing to lift the scaffold.
Fitting the dolly frame to the scaffold was a simple although I have no photos of it as I was concentrating on not screwing up. Basically I just tipped the scaffold over slightly on it’s long edge and slid the dolly frame under. I lifted the legs about 120mm and there was no danger of the scaffold falling over so it greatly reassured me that it also wouldn’t fall over in use.
With the dolly frame in place I couldn’t resist having a little play moving the scaffold around. Notice in that last photo there are pieces of wood between the top of the dolly frame and the corner braces. That is how the dolly supports the scaffold while it’s being moved.
The scaffold was quite easy to move although the small wheels did have a bit of a tendency to get caught in holes in the floor. The only mobility issue I had now was how to get the chocks in when putting the scaffold on the dolly. For the test move I lifted one end of the scaffold while the wife inserted the chocks. Clearly that wasn’t a long term solution as the scaffold weighed too much to be lifting it up all the time.
Step 9: Securing the Platform
The test climb showed that I really needed to fit something to stop the platform from moving. While it probably wouldn’t fall down in a hundred years the consequences of it happening were sufficiently bad that I wanted to do something about it.
After a bit of planning I settled on a simple little catch system made from a scrap of 18mm ply and a couple of bolts. The catch is nothing more than a P shaped piece of wood cut out with a jigsaw. At the focus point of the circular part of the P I drilled a hole for a bolt.
I offered the piece up to the bottom of the platform and aligned it such that when the catch was down it caught on the rung of the scaffold but it was still able to rotate up and free the platform to move. I then drilled a hold in the platform for the catch, this is the lower of the two holes in the photo.
Next, with the catch in place and in the locked position I drilled another hole above it, the top hole in the photo. Through this hole I slid a bolt which locks the clip in the down or locked position.
The nice thing about this clip is that the more the platform tries to slide out the tighter the clip locks. When it comes time to move the scaffold simply knock out the top pin and lift the clip. Since the clip would naturally fall down on it’s own and relock (default safe) I also designed it so that the locking pin can lock the clip open.
I fitted two clips to each end of the platform.
Step 10: Guard Rail System
Unfortunately the battery in the camera I was using ran out while I was filming the guard rail fitting so I’ve not got any photos / footage of that part of the build. The plans show the system I built though so not all is lost and I’ve grabbed some photos from the system in use.
The original design for my guard rail wan't workable so I redesigned it and that required fitting another rung right at the top of the legs and having the guard rail bolt onto the top and second from top rails. This way the guard rail can stay in place if and when I move the platform.
The guard rail system is quite simple. It comprises four 50x50mm uprights bolted to the top two rungs with strips of timber bolted around the top to stop you from falling off the scaffold. While the guard rails might not comprise many parts they do have to be made accurately because they are designed to be interchangeable on each corner and adjustable vertically. I started by rough cutting four pieces of 50x50mm PAR stock and then gang cutting them to exactly the same length.
Now mark exactly every 150mm up the legs from the bottom. Use a square to ensure the marks are in the same place on every leg. I chose 150mm spacings because the hole spacing on the rungs will be 300mm. Take the legs to the drill press and carefully drill though each leg at each mark. I used 10mm bolts to hold the legs to the tower as that was what I had on the rest of the scaffold and so I drilled 10mm holes.
Additionally at the top of the legs you want to drill one hole to attach a short rail piece and two holes perpendicular to the mounting holes to hold a long rail pieces. These holes should be for smaller bolts, 6mm is a good choice. With the legs finished it’s time to drill the mounting holes in the scaffold rungs. The holes have to be exactly 300mm apart and the best way to make sure that’s the case is to make a drilling jig. This is nothing more than a block of wood with appropriately sized holes but it’s important it’s made accurately to fit the holes in the legs – I suggest using the legs as a template.
In one photo you can see the guard rail in place and the demolition partially complete. I’ve got the platform down one rung from the normal working height and guard rails are down two holes from their full height putting the rail at about 1m above the platform. I was working right up in the low point of the pitch here which is why everything was set lower than usual.
There's also a few photos showing the guard rail system partially removed but note the adjustment holes up the legs which allow it to be moved up and down as needed. If you are wondering this is how I stored the scaffold at night and I took photos at the end of the work day. One photo shows the elongated grooves in the long guard rails. Initially I did this just to make fitting easier but it turned out to be a great advantage. Not only did it mean I could store the scaffold as shown in the photo but it also meant that when I was working in the pitch of the roof I could lower one end of the guard rail while leaving the other at the full height.
Step 11: Lifting Mechanism
With the guard rail system complete the only thing left to do was figure out some way to lift the scaffold a few centimetres so that I could get it up on to it’s dolly wheels. I tried a few different designs out before I settled on the one I show. All the designs had drawbacks and this one seemed like the least worst option.
The solution was to place a captive, movable beam under the second rung and then use a 5 ton jack placed on the dolly frame to jack up the scaffold enough to insert the chocks. What I didn’t like about this solution most was the captive beam. I cut it a fraction too short so it kept jamming as I slid it to one side out of the way. If I’d cut it longer I think I’d have liked it more. As can be seen from the photo below the jack could easily raise the scaffold high enough for the chocks and as it was on the short end there was no danger of it tipping over.
One moment of good thinking was to make the timber that captures the lifting beam a little taller than was needed. What this does is allow you to press down on the lifting beam once the scaffold is resting on the chocks to release the jack.
And that’s the build complete. If you liked this build please leave a comment below, I’m especially interested if you try and make one of your own. I really enjoyed this build and I can’t wait to try building another large project.