Building a Steel and Wood Shed: A Construction Diary
Building a New Garden Shed
Have you ever wanted to build your own garden shed? I always have and attempted my first one when I was about 10 years old, but abandoned the project because of lack of materials, skills and tools! Eventually, 40 years later, I got around to building a proper garden tool shed.
Although quite large, my workshop had become cluttered with garden tools, bikes and other miscellaneous stuff, and I needed more storage space. So it was time to build another shed specially for all this extra equipment. This article is a diary covering the details of construction and might help you if you are considering building something similar.
Stage 1: Clearing the Site, August 2015
The old shed had long outlived its purpose. Built in the late 40s or early 50s by previous owners, it was a patch work of corrugated iron, flattened out oil barrels and salvaged scrap timber, probably from the yard of a local man who used to collect this sort of stuff from demolished buildings. The roof was peppered with pinholes from corrosion and had leaked for years, however no amount of silicon sealant would fix what were now gaping cavities.
I thought it wouldn't take long to pull the structure down with a hammer and crowbar. However the builders had done a good job, using spiral shank nails to hold the corrugated sheets onto the timber frame. This is probably a lot more secure method of preventing sheet removal by burglars than using TEK screws.
Stage 2: A New Year, 2016 and Back to Work on the Project
Cold, wet weather and incessant rain during the autumn and winter of 2015, getting side tracked by other chores and duties and a series of personal events led to abandoning the project for the rest of the year. I eventually got back to clearing the rest of the shed in February. The corrugated iron was bedded down under the concrete floor and had to be prized out with spades, crowbars and cut with an angle grinder.
Step 3: Starting to Concrete
June 1st, 2016
The existing concrete floor was at two different levels. It was partially cracked also and didn't have a vapour barrier which meant the air in the shed was always damp, with lots of condensation on the underside of the corrugated roof on cold mornings, which inevitably dripped down over everything. I decided to break up the cracked section of concrete which resulted in a large pile of rubble. I would also lay a new floor on top of the remaining concrete section, but make it thicker at the edges for structural strength. The new shed would be several feet longer and wider than the existing one. This resulted in having to excavate lots of soil which needed to be spread out over the garden, under trees, into hedges and basically anywhere I could find space.
I roughly marked out the corners of the shed with 1/2" (12 mm) rebar and marking paint. Firstly I hammered two pieces of rebar into the ground to mark the front wall, knowing the length of the planned shed. Then I roughly positioned the 2 bars for the back wall knowing the width of the shed. Knowing the length and width of the shed and using Pythagoras's Theorem, this gave me a measurement for what the diagonal length should be between opposite corners. This established the footprint for the shed.
Stage 4: Dealing With a Particularly Temperamental Cement Mixer
The Belle mixer had been thrown out but rescued several years ago from a scrap yard. It was minus a stand so I built a new tripod out of 1 1/2 inch gun barrel, 2 inch box, a short piece of round solid bar and some flat steel. It didn't have an engine either. Modern Belle mixers are usually driven by a Honda or Robin engine but I decided to use the engine from my old Suffolk Punch cylinder lawn mower as a replacement. But little did I know what hardship was ahead of me! The float bowl on these engines tend to drip eventually, but because the engine was mounted at a 45 degree angle on the drum, the bowl was never vertical, so the float never sealed properly. The result was lots of petrol drips during mixes. Next problem was the drive belt started slipping during a mix, with another mix ready in the wheel barrow and a third mix spread out on the ground! Very frustrating! Eventually the engine stopped working and refused to crank. I opened it up and discovered that the splasher on the crankshaft had broken off. So the engine was running dry with no lubrication. This damaged the connecting rod and smeared aluminium over the crank shaft. I made a new splasher, but eventually when the concrete floor was almost complete, a large bang signalled that my 'trustworthy' engine had definitely reached the end of its life this time. A post mortem revealed that the connecting rod had broken up into 5 pieces. The last section of concrete had to be mixed by hand.
Stage 5: Building the Formwork and Laying Concrete
Building the Formwork
I decided to lay concrete in six sections. I used two-by-fours (2 x 4) for the form work (the timber "shuttering" or mould into which concrete would be poured). This shutter consisted simply of a rectangle, nailed at the 4 corners. For the long walls, 2 x 4 had to be joined with short 2 x 4 scraps because the lumber wasn't long enough to extend the full length of the side. At the corners, nails weren't driven home so that the formwork could be easily disassembled later with a crowbar without damaging the concrete it surrounded. Thinner boards can be used instead of 2 x 4, but 2 inch thick timber requires less pegs to hold it in place because it doesn't flex and bow as much over a long span.
What's a two by four?
A two-by-four, (2 x 4) or four-by-2 (4 x 2) is a piece of rough, unplaned lumber (wood or timber) with a cross-sectional area of approximately 2 inches x 4 inches (also written as 2" x 4", the quotes meaning inches). Typically these are available in lengths from 4 feet to over 20 feet long. It's a popular size, used for constructing stud walls (framing), bench frames and other general construction. In countries that use the metric system, these are sometimes a bit thinner than 2 inches. (44mm by 100mm).
Getting the Formwork Square
With the formwork constructed in place and two rebar pegs hammered into the ground to mark the endpoints of the front wall of the shed, I dragged the frame into position so that its two end corners coincided with these pegs. Then knowing the width and length of the shed, I was able to calculate what the diagonal lengths should be using Pythagoras' Theorem. Using two tapes stretched between opposite corners of the formwork, I altered its shape until the diagonals were equal. This is pretty much essential if you want the footprint of your shed to be rectangular and not skewed. If you don't do this, you'll run into problems later with everything off square and for example, roof sheeting will be crooked. I then hammered rebar into the ground to mark the two back corners and tied the four corners of the frame to the four pieces of rebar. Next I hammered pieces of 2 x 1 at 6 foot intervals into the ground and after levelling the formwork, nailed it to these pieces. This prevented any sideways or up and down movement.
I had kept the existing floor from the original shed and used this as foundation. However if you intend to lay a floor, you need at least 4 inches of sub-base rubble to act as a foundation, topped with sand to stop the stones piercing the moisture barrier plastic. The ground is dug out beforehand so that this sub base is flush with the ground. 4" (100 mm) of concrete is plenty strong for a garden shed with no vehicular traffic, but 6" (150 mm) is the minimum for concrete that is going to be driven on.
1200 gauge polythene sheeting was used under the concrete as a moisture barrier. This makes for a really dry shed. If you don't use a damp proof barrier, moisture rises through concrete and on a frosty day it can condense on everything. The floor was constructed in six, 1m (approx 39") wide strips.
Stage 6: Erecting the First Wall
Walls were constructed from 2 x 4s. Treated 2 x 4s were used for the bottom plates in contact with the concrete. I nailed on 4" damp proof membrane with galvanized slab nails to give the timber additional protection from rising damp. It's recommended that studs are spaced 16" (40cm) apart for sturdy construction. 4" (100mm) round wire nails were used for nailing the studs to the top and bottom wall plates, a pair for each stud, top and bottom.
- Window header
- Top plate / upper wall plate
- Window sill
- Bottom plate / sole plate / sill plate
Stage 7: Erecting a Second Wall
All work was done single handedly and while walls were not excessively heavy, some thought had to be put into rising them into place. Quick release clamps placed at strategic locations at arms reach allowed me to clamp on lengths of 2 x 4s to act as stays to keep the walls in place. Once this was done, the stays could be nailed into place to make them more secure.
Stage 8: Four Walls in Place
Four walls erected and ready for top plates. Notice the 1 x 2 diagonal braces. These were added to keep everything square. Should have cut the overhanging apple tree first. Removal was a bit awkward to avoid demolishing the walls!
Stage 9: Adding the Roof
Once the top plates were in place, it was time to build the roof. On advice from carpenters on a building forum, I decided to use 2 x 7s for rafters. Snow load can potentially amount to tons of weight on a roof. Birdsmouths were cut using a circular saw and reciprocating saw and waste chopped out with a chisel. Rafters were then toe nailed to the top plate at the front and back walls. Toe nailing means skewing the nails or hammering them at an angle so they're less likely to pull out.
Birdsmouths or notches had to be cut out of the ends of the rafters to allow them to rest on the top plates.
The rafters were later more securely attached to the top plate and studs with "Galvoband", perforated metal strapping. These act as ties, potentially stopping the roof being lifted off the walls during a storm.
Stage 10: Adding the Fascias
I decided to use 2 x 7s for the fascias. Stronger, more chunky and less likely to warp than 1" boards. Before nailing fascias onto the ends of the rafters, I treated the latter with creosote substitute as a preservative. The fascias were nailed with galvanised 4" nails. Blocking (nogging) was used on the end walls for spacing the fascia. Quick release clamps held the boards in place until they were nailed.
Stage 11: Bracing the End Walls
Strong winds always blow from the south west and these would hit the front walls. I braced both short end walls with a "V" layout of 2 x 4s meeting at the ground and bolted to the corners of the walls.
Stage 12: Adding Underlay to the Roof
I sourced a permeable membrane from Screwfix.com to act as an underlay under the steel cladding. Smooth, cold surfaces attract condensation. The underlay catches any condensation drips from under the sheets, carrying it to gutters. Also its underside has a rough woven texture, so water vapour in air landing on the underlay doesn't condense. Without this, on a frosty day, the underside of un-insulated steel cladding can get covered with condensation which ends up dripping over everything.
Stage 13: Cladding the Roof and Walls
Once the roof was covered with underlay, it was sheeted with painted, square profile, galvanised steel cladding. This is really supposed to be fixed to laths nailed or screwed to the roof/walls, however I fixed it directly.
Stage 14: Adding a PVC Fascia
After giving the 2 x 7 timber fascia a couple of coats of wood preservative, I clad the timber with PVC fascia so it would mean one less painting job to do in the future!
Stage 15: Constructing the Door
The door frame was constructed from 2" x 1" steel box and inlaid with all the waste 4 x 2 cut-offs from construction. Flat strips of steel top and bottom, inside and out kept the boards in place. These were tack welded at regularly spaced intervals so water could drain out between the welds. Angle section steel can of course can also be used to construct a frame although box results in a more rigid door.
Stage 16: Making the Door Hinges
Hinges were made from scratch from 6mm x 40mm flat steel, steel tube and scrap round steel bar from my local steel fabrication company.
Stage 17: Hanging the Door, May 2017
Hanging the door was somewhat tricky. I reckoned it would be quite heavy (it eventually turned out to be 10 stone), so I decided to hang the frame first before inlaying all the 2 x 4 panelling. Two hinge hanger parts were bolted to the timber door jambs first, then the frame of the door was clamped onto the other parts of each hinge. The clamps were then adjusted so that the door was spaced properly in the opening with an even gap all round. Next I took the door down again and welded the two hinge parts to the frame. With everything rigid and not likely to move, I rehung the door onto the two hinges, bolted the third hinge on and took it down again and welded it.
After fully panelling the door, it was time to rehang for the final time. This was very awkward, because three hinges had to be aligned simultaneously so the hollow hinge parts on the frame could be dropped into place. Ropes were fixed to the top of the door for safety to restrain it from toppling as I worked on the ground to raise the door bit by bit onto blocks of wood. Once the hinges parts on the jamb and door frame were level, I was able to slide the door sideways and allow it to drop into place.
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This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2019 Eugene Brennan