Shed

Construction

While there are many ways to build sheds, the great majority are wooden and contain the following elements:

• Base
• Floor
• Frame
• Cladding
• Window
• Door
• Roof sheeting
• Felt

(Base and floor functions are sometimes separate, and sometimes both performed by the same item.)

Base

In each case where a timber frame rests on masonry, its best to put a damp barrier between base and timber. A roofing felt offcut can be used for this. These barriers are often omitted, but can reduce the tendency to rot.

Poured concrete base

• a very durable permanent structure

Construction:

• 4" concrete recommended
• 3" is a lot weaker, but sometimes used
• Concrete usually laid on compacted ground & hardcore
• final concrete level should be above ground level
• See Mortar Mixes

Damp:

• Concrete conducts damp
• A DPC within the slab is not necessary, but can keep the shed interior drier
• a waterproofing admix might also work

Brick or block piers

• used for suspended timber floors
• the risk of a pier or 2 sinking is always present
• pouring a small concrete pad for each pier reduces this risk

Concrete fence posts, horizontal

• A quick easy option for use with a suspended timber floor
• cost higher than blocks
• Ideally use weed control fabric due to low clearance

Paving slabs

• quicker than a poured base
• some risk of unevenness occuring over time
• the joints let in some damp
• Joints may be tarred to reduce damp ingress
• slabs are usually laid on compacted sand

No base

• Not recommended, lets in significant damp, and encourages wood rot
• damp spoils stored goods.

Floor

Concrete base

A concrete base also acts as a floor.

Suspended timber floor

• WBP plywood recommended
• Chipboard is totally unsuitable

Frame

There is no one answer to the question of what size framework to use. Any of the following can be used, and which is best is a matter of opinion and circumstance.

• 1"x1" is the lightest I've ever seen used for smaller sheds. The walls would bend when leant on
  • Would not support shelving
  • Would not last too well
  • Not recommended!
• 2"x2" is light but adequate for a small shed in a fairly sheltered location.
• 2"x4" is a robust option
• 3"x3" or 4"x4" may be used for large sheds or for extra durability on medium sheds.

Restraint

Rectangular timber frames can twist and fall over if not restrained. Movement pulls the fixings apart, permitting further movement until the structure falls down or leans. Some form of restraint is necessary.

Timber bracing is the usual method, either with small or large bracing.

Sheds built onto 2 masonry walls will be restrained by those walls, and need little bracing. Sheds built onto one masonry wall still need some bracing.

Effective bracing needs to be done on at least 3 sides. 2 side bracing does not rigidify a frame structure. Maximum strength is achieved by bracing all sides.

Masonry sheds don't need bracing, but often need piers to ensure wall stability.

Methods:

Large timber bracing

• Each square frame is braced with a strip of wood running from one corner to the opposite corner.
• Simple
• Gets in the way of insulation, some shelving and hanging tools

Small Wooden bracing

• Each 90 degree timber joint is reinforced with a short piece of extra timber at 45 degrees
• no extra material cost
• less intrusive

Steel brackets

• London brackets are a quick ready made option
• These stiffen the structure, but generally arent as tough as timber bracing.

Cladding

The frame may be clad with various options to give a closed structure.

Featheredge boards

• the most common option
• medium durability
• gaps at corners allow airflow, draught & insect access

Shiplap

• neater higher cost option
• no gaps, not draughty

Fence panels

• a quick low cost option
• the shed must be sized to fit the panels used
• less durable than featheredge
• not very strong, a security issue

Planks

• 1" plank gives a very tough durable building.

Window

• Sheet glass
  • breakable
• Sheet plastic (acrylic)
  • less easy to break
  • can deteriorate in time
• Twinwall polycarbonate
  • Insulates
• Reclaimed house window

A shed window is usually a simple rectangular wood frame with a small section wood strip around the inner side to prevent the glass moving inward. A few panel pins around the edge hold the glazing in place.

Wood beading can be used instead of pins, but by trapping water this encourages rot in the frame.

Reusing a house window works, but tends to look rather out of place, and creates extra work if the glass gets broken.

Door

Ledged & braced is by far the most common shed door construction

Timber:

• T&G is usually used, but any thin planks are usable.
• T&G avoids gaps opening up due to warping
• When not using T&G, additional light bracing is recommended to address warping
• the horizontal ledges may be 2x1.5 or bigger
• bracing may be 2x0.5 or bigger

Construction:

1. The thin planks are laid side by side.
2. They are screwed or nailed to 3 wood strips (ledges) running across, one at the top, one at the bottom, and one halfway up the door
3. 1 or 2 bracing strips are added at an angle on the inner side of the door to prevent it drooping on one side

Roof sheet(s)

The options are:

• timber roof sheets plus felt
• corrugated sheet, available in various materials

Pitched roofs should overhang the shed. This way they shed rain water away from the walls, helping prevent rot.

Timber roof sheets

• WBP ply - maximum durability
• OSB - nearly as good as ply. Most common choice.
• Chipboard
  • cheap
  • works but will give slightly shorter life, as it disintegrates fairly quickly when a leak occurs
  • prone to sag
  • more care is required with roof detailing, as any water ingreess at all will quickly cause chipboard disintegration

Felt

2 layers of roofing felt are used for durability.

Low cost shed felts tend not to last well, and are generally a false economy.

Felt deteriorates quickest where it goes over edges, so taking care over sheet wood joints can prolong felt life.

Felt is held in place by folding it over the edge of the roof and using clout nails. Self adhesive felts are also available.

Better alternatives to felt are available, but carry a much higher price tag, not usually justifiable for shed construction.

Corrugated roofs

Corrugated sheet is available in various materials, including:

• clear plastic
• opaque plastic
• composition (eg onduline)
• Steel
• fibre cement

Clear plastic eliminates the need for other windows, but makes for a very hot shed in summer. A white shower curtain may be fixed underneath to reduce this effect to some extent, and prevent people seeing into the shed.

Plastics and composition sheets are low strength and need good support from battens.

Metal roofs can be noisy in rain, which is a consideration for sheds that will be usd as workshops. Some people aren't concerned by a little noise, some are.

Construction

All corrugated materials are fixed by screwing through the sheets and into the timber (or sometimes metal) frame. Screws with pre-attached soft caps are used, the cap material squashes and makes the join watertight.

Sharp pointed screws are used for timber and lightweight steel frame, self drilling screws are used for most metal frames.

The edges of corrugated panels are overlapped to maintain watertightness. For larger roofs, panels are fitted at the lowest part of the roof first, with the next layer overlapping these.

Corrugated panels create large gaps at the ridge line, and the ridge is capped with any of:

• purpose made matching capping sheets - eg onduline
• lead flashing

Timber Species

Softwood (eg spruce)

• most popular
• low cost
• requires periodic preservative
• rots eventually

Red cedar - much more durable

Oak - rarely used but highly durable. Can last centuries

Optional Extras

Frame Reinforcement

• Increases robustness against high winds by reinforcing framing joints
• Resists nail pullout at joints

Steel strapping

• Perforated galvanised metal band is wrapped around joints and nailed in place
• Useful in high wind exposed locations.

Bracing

Any type of bracing will toughen the frame considerably. This is usually the best way to go, as it rigidifes and strengthens in one go.

Insulation

If the shed will be used for working in, polystyrene sheet may be fitted between the frame members. When using featheredge boards, which leave gaps, a permeable membrane should be used between frame and exterior boarding to prevent draughts.

Shelving Racks

See Shelving Units

Lighting

Lighting may be achieved with:

• Gas lamp
  • minimal install cost
  • ventilation is wise (the usual featheredge sheds provide ventilation)
• Mains Electricity
• Solar panel, battery, 12v striplight
  • easier than mains installation
  • panel can be vulnerable to vandalism
  • can recharge cordless tools of upto 12v

Waterproof Base

A waterproof concrete mix for the base can reduce damp levels in the shed when these bases are used. Coating the base is also an option.

Fixings

• Galvanised nails are the usual option
• Screws hold better and are more robust in areas prone to high winds or vandalism.
• Glued structures are not recommended

Other Construction Methods

Most sheds are timber, but various other options also exist.

Common options:

• Concrete block
  • permanent structure
• Metal
  • fireproof
  • dents & rusts
  • expect condensation
• Plastic
• Fibre cement sheet
  • long lived but not cheap
  • pre-1986 fibre cement usually contains asbestos

Unusual options:

• Papercrete
• Cordwood
• Adobe
• Earthcrete
• Concrete domes

See Also

• Wiki Contents
• Wiki Subject Categories