Build Your Own Summerhouse — Part 1, Groundwork

Stage 1 — Groundwork

A summerhouse is something I’m sure many people would love to have in their gardens. However, the choices for buying one seem to be “cheap and flimsy” or “substantial and extortionately expensive”. We decided I could make one myself. It is the biggest project I’ve ever undertaken but it has been immensely satisfying and the result is far superior to anything we could afford pre-built.

This is the first of a series of posts outlining the summerhouse build spanning the last 12 months. That might sound like a long time but the majority of it happened in two weeks last Easter. The rest of the work was done on odd weekends and evenings since then. It’s actually still not finished. I plan to split the posts up into logical stages: groundwork, framing, roof, etc. So you can adapt the design to your own needs, I will do my best to explain what I did step by step and the logic behind the decisions.

Planning

It’s only fair to say that during the groundwork stage I leaned heavily on a fantastic book I bought from Amazon called “Building Sheds” by Joseph Truini. I wanted to make sure I got the foundation right, having never built a structure this big before. I will be outlining how I did mine here but most of the technical information came from that book.

A rough sketch of the initial overall look I was going for. I later decided not to have the fence and posts at the front. Instead, I went with a cantilevered roof and planters as a border to the veranda.

First of all, you need to decide how large you want your summerhouse to be. The size will ultimately affect many of the decisions you make going forward on shape, materials, foundation type and of course, it will influence the costs involved. The footprint of my summerhouse is 4.2m X 3.2m (14ft X 11ft). A non-permanent foundation of dense concrete blocks and gravel can support a structure this size. This choice of foundation also helps to avoid the need for planning permission in the UK.

Tip: When you decide the size of your summerhouse, use standard lengths of timber and sizes of sheet material as a guide. This will save money and reduce waste.

Stacked concrete blocks seated on a bed of gravel support a strong timber framework, simply and effectively giving a base for the rest of the structure. Choose the locations of the gravel pits and blocks to best support the timber frame. The corners are critical and the spacing will depend on the thickness of the floor timbers used. For my floor joists, I used 47mm X 150mm (2" X 6") treated, regularised and graded timber; blocks were then spaced between 1.2m and 1.5m apart. I originally planned to use smaller sections and layer them up; I changed the design after creating these sketches.

Sketching things out helps you to think things through.

Layout

Marking out the ground with the eventual locations of your blocks is important before you start digging. Long pieces of timber or cord can make this stage easier and of course you’ll need a decent tape measure. Before you make your final decision on location, think about nearby trees and bushes and how they might affect your summerhouse once it’s completed. The way I did this was to lay timber on the ground in the shape of the overall floor frame. To check if the shape you’ve laid out is square in the corners (assuming that’s what you want), measure it diagonally and check the results match. Draw a perimeter on the ground using line marking spray.

While you’re marking the lines, get a feel for any gradient or dips in the soil. This will help later.

Once you have a perimeter drawn on the ground, lay out your blocks according to your plan, remember to keep them inside the perimeter. Mark around each block with at least a 2-inch border using the line marking spray. This is where you will dig your holes so also clear away any fallen branches or debris.

Remember to lay the blocks inside your floor frame perimeter to maximize support and aesthetics.

Digging

Making holes in the ground is pretty straightforward but definitely exhausting. Here in Yorkshire, the ground has lots of pieces of stone so getting a post hole digger made it easier. These are also good for chopping through small to medium-sized tree roots. You’ll also obviously need a spade and a shovel can be useful for clearing out the soil.

This job can be really hard on your back, getting help from your wife is highly recommended.

You’ll need to dig down about 4–6 inches for each hole. Try to keep the sides of the holes sharp and vertical. Avoid damaging the main roots of trees and bushes you plan to keep but cut out any small roots growing under or near your holes.

Try to make the sides and bottom of your hole sharp and firm. So to speak.

Filling

Before you start to fill the holes compress the soil at the bottom as much as you can. Use a tamper to do this, or if you’re saving money you can do a decent job stamping it down with your foot. Fill each of the holes with 10 or 20mm pea gravel, either should be fine. Fill the holes all the way back up to ground level and make sure it gets right into the corners. I found that 6-inch deep holes, based on a 2-inch border around a standard dense concrete block, took 2kg bags to fill… ish.

Once your holes are infilled with gravel and a block is in place, there should be a good clean 2-inch border of gravel all the way around the block.

Levelling

Perhaps the most technically difficult and frustrating part of the groundwork stage is levelling the tops of all the blocks. I could have course levelled the actual ground before starting but that’s a huge amount of manual labour if you don’t have a mini digger, which I don’t (yet). It is, however, really important to do a good job of this to avoid headaches down the line.

The basic premise is to start at the highest corner and lay a long straight edge between the blocks, with a spirit level set on top of it. There are many, perhaps better, methods for getting things level but this worked for me. If a block was too high I removed a small layer of gravel; if a block was too low I added some gravel. In some places, the ground was so much lower I added another block, one of them even had three blocks. You can also use mortar between the blocks to fine tune their height. I used this technique for one of my stacks that proved difficult with only the gravel and multiple blocks method.

Work from a reference corner to avoid cumulative errors in “level-ness”. The highest corner would be my choice as it is easier to raise the blocks than lower them.

Costing

Groundwork can often be one of the most costly stages in a big project like this. This method helps to keep the costs down and has the added benefit of being reasonably easy to achieve.

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Summary

This stage will take a while and not look like much at the end, don’t feel discouraged. Groundwork is the literal foundation of your structure and getting it wrong means everything that follows is at risk. It is essential to the final quality of your summerhouse.

Next, I will outline the floor frame which could also perhaps be considered part of the foundation. Once that post is complete I will add a link to it here.

Originally published at Crin Makes Stuff.