building a summer house

Building a Summer House

How to build an outbuilding in less than a month that would pass building regs like a house!

If you’re following us on instagram or facebook, you’ll see what else we’re up to whilst waiting for planning permission. We’ve been getting the outside areas ready to go and building a summer house in the garden too!

Initially, this involved garden clearance and some landscaping. Albeit more than we expected due to many rotten trees and dangerously overhanging branches.

However, ripping out more than we’d anticipated from the garden paved the way for us to build a summer house at the end of the garden. Have you ever thought about building a summer house? Well, it was a first for us. Ordinarily we would order a summer house that is supplied and built by specialists. On this occasion though, given our exacting requirements, we decided on a DIY version. This was because we wanted it bespoke to our size requirements and intended use. Destined for a gym, we needed a solid floor base to withhold weights being dropped and pounding from gym equipment.

But first things first…

If you’re going to build your own summer house, do you require planning permission?

Well, ultimately this all depends on the size and purpose of your summer house. Outbuildings are allowed under permitted development, not requiring a planning application, provided these following conditions are met:

  • Outbuildings must not exceed 50% of the total area of the land around the original house
  • Any new building must not be used for living accommodation
  • It can only be single storey with a max eaves height of 2.5m and max overall height of 4m with a dual pitched roof. Or 3m in any other case (e.g. 3m max for a flat roof)
  • Must be 2m in from the property boundaries on all sides (otherwise height restriction reduces)
  • Balconies/verandas aren’t allowed

There’s a few other considerations if you’re building an outbuilding, but above are the key ones for a residential house.

Landscaping a garden

Given we’re lucky to have a huge garden, we can therefore build away size-wise to our hearts content. And this is part of the reason why we chose to build it ourselves so we could build it to our exact size requirements. We could optimise the space whilst staying 2m in from the boundaries, and respecting the 3m height limit.

With a plan in place…let the build begin

The steps to building your own outbuilding

The below steps are for building a timber framed summer house or outbuilding. However, bear in mind ours will be all done to a high spec suitable for a gym. A solid sub-floor. A fully insulated space for warmth and electrics for gym equipment. Although it won’t be used as a habitable space, the spec is building reg compliant as if it were a home. From the foundations to the damp-proofing to the insulation! I’ve also outlined below for your reference how many days it took to build. Bear in mind these are ‘working’ days, you’d need to factor in time for setting/drying too.

Day 1 – clear and level the area

We hired a machine driver for the day to dig out everything on the ground. This included ripping out dead tree roots and scraping / levelling the ground ready for the base.

Day 2 – build your frame & damp-proof

Preparing the base of an outbuilding

The frame base surround was built into the ground with 8 x 2 treated timber. Inside the frame the ground was then filled with 100mm Type 1, levelled and compacted with a whacker. A layer of damp-proof membrane was then laid across the whole floor base. Steel meshes were then placed on top of the membrane raised by castles. This was to ensure the mesh doesn’t touch the membrane. Thus, the concrete will be able to flow underneath the steel mesh when poured.

Preparing to pour the concrete

Day 3 – create the concrete base of the summer house

The floors then had 100mm of outside liquid screed pumped in and levelled. This was then left to set to create a proper solid base with damp-proofing underneath.

Pouring the concrete foundations

Day 4 – engineer your summer house out the ground

With a solid base in, what is next when building a summer house? Next stage is to engineer it out of the ground. A brick layer came in to engineer it up to damp course level (with engineering bricks). It is then ready for the timber frame to be built on top. A layer of damp course is laid on top of the bricks.

Days 5-6 – build the timber frame of your summer house

The timber frame of the summer house was then built on top of the engineered brick and damp course. This comprised of 6 x 2 timbers all around, allowing gaps for any windows and doors. The walls are then ply-lined with WBP (water-based ply).

Building a summer house

Days 7-8 – get your summer house in the dry

With the timber frame walls up, you can focus on getting it in the dry. Likewise the summer house roof is constructed with the same 6 x 2 timbers. Firrings are then laid on top of the new roof joists which create a slope. This is necessary when you’re putting in a flat roof so that rain water can fall off. 18mm OSB boards (oriented strand boards) are then placed on top of the firrings. This is followed by 3 layers of roofing felt for the finished roof. OSB is increasingly used over plywood as it’s stronger.

Timber construction outbuilding

Arris rails were then attached along the front, back and sides of the building to also ensure rain fall off. Soffits and fascia boards are put up around all the edges where the roof meets the external walls. This is to support airflow and the guttering. 

WBP is then used to form the external walls, attached to the frame of the 6 x 2 timbers. A breathable membrane is then battened in to place on top of the WBP on all sides of the house. It’s now ready for whatever cladding we decide to add for the finishing touch externally. We’re holding fire on the cladding at present as we want to match the cladding in with the house.

Building a summer house

Day 9 – door & windows

The last step to then get your summer house in the dry is to install the doors and windows. Now the building is secure too so we can start to store things in it.

Building an out building

Days 10-11 – internal flooring of your summer house

If you’re building a summer house more as an outdoor shed you can of course simplify the build. You could just build it out of timber on top of a level patio surface without damp-proofing or insulation. This will certainly be a lot quicker and much less costly if you’re just using it for storage. However, we always like a solid build to ensure no damp gets in. Also, if you want to be using the outbuilding as an office or functional room you’ll want to go the extra mile. You’ll require warmth and damp-protection so that you can to decorate it. Our steps for sure will future-proof it for the long term and multi-functional purposes.

With the summer house now in the dry, we can finish the space internally. A layer of damp proof membrane is laid across the entire floor and lapped up the walls. 100mm insulation is then laid across the floor, then a second layer of membrane laid on that. Finally a 75mm top layer of sand & cement screed is pumped in on top. It has an accelerator mixed within it so that it cures (sets) quickly. Otherwise it would take c. 1 day/mm to dry, depending on weather conditions. This would mean several weeks to dry – not happening!

Days 12-13 – internal walls, ceilings & first fix electrics

Insulating a room

We then insulated the walls and ceilings internally with 100mm RWA 45. We didn’t use kingspan primarily as it’s just a thermal insulation. RWA however is fireproof and also offers sound proofing insulation as well as thermal. 

If you’re building a summer house you must also consider what electrics/plumbing may be required. Just bear in mind with plumbing that could then fall in to the category of a “habitable” space. Which may then require some form of planning permission, so consider this carefully versus your intended use.

With internal walls now built and insulated, our electrician was then on site. This is perfect time for your first fix electrics allowing for lighting requirements and sockets. 

There will be 100m of armoured cabling going in and 100m of data cabling. This is to ensure we can have full functioning wi-fi/internet in the summer house. As primarily intended as a gym, we had to consider the requirements of modern day equipment. This often requires internet connections nowadays to join virtual classes or the likes. We’re also going to have a “chill” area in the corner with a TV as a teen hang zone, so smart connectivity required. All electrics will need to link back to the fuse board in the house.

Plaster boarding a room

We then boarded the ceiling with 12.5mm plasterboard, and boarded the walls with MDF. We also used 3 x 2 timbers to build a stud wall for a cupboard. This was likewise boarded with MDF. We could have plaster-boarded the walls but we needed more strength. We want to be able to put TVs, mirrors, pictures and the likes up on the walls. MDF will be stronger to accommodate this. The electrics were pulled through then the walls and ceilings were all skimmed ready for painting.

Building a summer house

Electrics were also pulled through externally in readiness for outdoor lighting. As I write, we’re just waiting for a final visit from the electrician to fit these too.

External lighting on an outbuilding

Days 14-15 – Final touches and decoration

Last stage now on our step-by-step guide to building a summer house. The smooth, skimmed walls are now crying out for a touch of paint so the decorator has been in to give them some colour. We used Dulux trade paint, and had this colour matched to the Farrow & Ball Strong White and Off Black.

Later update: the electrician has since been out to second fix the lights and socket plates.

We also made a last minute decision to add skirting and architrave to finish the look. These were subsequently painted and two electric heaters fixed to the walls.

Internal finishes in a summer house

So in around 3 working weeks you can build your own timber summer house or outbuilding. This is from scratch, with full damp-proofing, insulation and electrics. If my husband was quoting this for a customer, he’d probably allow 3-4 weeks, subject to weather.

Our garden summer house

From our side we’re now all finished. We added Teckwood perennial composite cladding in tudor black to the external walls. This is European Class B fire-rated and a great long-lasting, low maintenance alternative to timber. And can you spot another difference? We painted the door and window frames black to blend in. Yep, I realise, I should have just ordered them black in the first place. We all live and learn.

Composite wall cladding

And our son has now turned it in to a gym!

Home gym in the garden

Together with a bit of landscaping, returfing, and a resin pathway, the garden is now officially complete.

Building a summer house

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