How to Build a Summer House Base – Step by Step Guide & Ideas

Key Considerations for Building a Durable Base for Your Summerhouse

Building a quality base for your summer house ensures it remains steady, level, and damp-free. This in-depth guide provides detailed instructions on how to do it.

Ultimate Guide To How To Build A Base For A Summer House

Summer houses are a quintessential addition to classic British gardens. These sanctuaries allow you to enjoy the seasons in all their glory while offering protection from the sun, wind, and rain.

However, if you want your building to last, learning to build a base for it is essential. If you don’t, it could rot from the ground up, fall over, or become a victim of the wind.

Fortunately, you don’t have to figure out how to build a base alone. This guide is here to help. It covers the types of bases for garden buildings, how to construct your base, the best people for carrying out base construction, and various tips for repairing and maintaining your installation. It’s everything you need in one place.

Why Summer Houses Need Bases

When constructing garden buildings, bases are essential for stability and longevity. The structure is susceptible to shifting and settling without a solid base, leading to potential damage over time.

Bases provide a level surface for the building to sit on, ensuring that weight is evenly distributed and reducing the risk of structural issues. Also, bases help elevate the building off the ground, minimising contact with moisture and preventing rot and decay.

Overall, investing in a proper base is crucial for the integrity and durability of the summer building. However, they still require a base, a high-strength structure that ensures they continue functioning long-term. Without it, they won’t last.

Longevity

The primary reason for building bases is to ensure structure longevity. Constructions offer moisture protection, stopping dampness from the ground from percolating through the summer houses’ wooden floors and walls.

Keeping the structure dry reduces the risks of rot, mould, and structural warping, making the building more straightforward to maintain.

Level Ground

Bases also provide summer houses with level ground. Professionals build these to make a flat expanse, allowing the building to sit straight.

Without a summer house base, they would be reliant on the flatness of the soil beneath them. The ground would have to remain perfectly level throughout the life of the construction to keep it straight and true (which would be highly unlikely).

Bases prevent one side of the summer house from sitting lower or at an angle from any other. Like foundations for conventional homes, this keeps the structure upright.

Stability

Finally, bases offer stability. Hard materials, such as concrete or paving slabs, stop the building from rocking when people move around inside.

Types of Bases for Garden Buildings

Garden buildings use various bases to keep them level and stable. Your choice will depend on your priorities, climate, and other factors.

The following are the three main base types available. We discuss them and the pros and cons of each. By the end, you should have the data to decide which option is most appropriate for your project.

Concrete base

Concrete bases are solid slabs poured onto the ground (usually into an excavation). Installers use special tools to ensure the material sets smoothly, providing a secure base for the summer house to rest on.

Pros:

• Highly stable and durable. Concrete is an ultra-hard-wearing material suitable for outdoor use in exposed areas. It works particularly well for heavy outbuildings, including summer houses.
• Long life. Most concrete bases last for decades. (Some property owners are still using concrete platforms built during WWII). Once installed, it will often outlast the building standing on it.
• Little to no maintenance. Concrete bases do not require treatment. Once in place, maintenance is helpful but not essential.

Cons:

• Drainage issues. Concrete slabs can accumulate moisture underneath them that can percolate into the material over time due to tiny, porous holes.
• Harder to install. Professionals do not recommend DIY concrete base installation. Construction requires numerous complex steps, including excavation, land preparation, curing, and levelling. Furthermore, fixing mistakes is challenging and requires breaking up the concrete and reinstalling it.
• Costly. Concrete bases are more expensive than most alternatives (due to the material and labour costs).
• Time-consuming to install. Summer house owners must wait for concrete to set fully before placing the building on top. This process can take days or weeks, depending on the product.

Paving Slab Base

Paving slab bases are simpler and made of slabs laid on crushed aggregates, like gravel, or no sub-base (not recommended). These offer many homeowners an aesthetic they love but without the sturdiness of concrete.

Pros:

• Easy to adjust. Installers don’t need to lay paving slab bases perfectly the first time. DIYers or professionals can play with each stone and the aggregate underneath it until everything falls into place.
• In-built adjustability. Owners can move paving slabs over time, reacting to ground density and subsidence. Sub-bases are easy to re-level for paver relaying.
• Faster installation. Installing aggregate bases and paving slabs can’t be done without special tools or equipment. Groundwork is still necessary, but concrete is more involved.

Cons:

• Less stable. Paving slabs may move and rock if shifts occur in the sub-base, causing any garden buildings to become less stable.
• Higher maintenance. Concrete bases remain the same throughout their lives, while paving slabs can migrate or change the height. Depending on the surrounding landscaping, owners may need to re-level paving slab bases periodically, increasing maintenance requirements.
• Sub-base drainage issues. Paving slab aggregates may not allow water to drain properly into the surrounding soil (especially as they age). Sub-bases may need replacement (which would involve lifting the slabs, refilling the excavated area, and replacing them).

Timber sub-frame base

Timber sub-frame bases are made from treated wooden beams on concrete pads or foundations. Summer houses perch on top of these, reducing the risk of moisture damage.

Timber sub-frame bases were more popular in the past when the material was readily available. However, it usually requires constructing a concrete supporting structure.

Pros:

• Suitable for light soils. Wood bases weigh less, making them more suited to softer soils.
• Cost-effective. Summer house owners can add wooden beams to existing concrete work, reducing installation costs substantially.
• Easy to install. Timber sub-frames do not require curing or drying time.

Cons:

• Normally requires concrete pre-installed. Most timber sub-frames require pre-installed concrete pads or pillars to work effectively. Others require brickwork to provide a barrier with the underlying soil.
• Poor durability. Timber doesn’t last as long as concrete due to its susceptibility to moisture, rot, and burrowing insects.
• High maintenance requirements. Timber sub-bases require ongoing treatment with preservatives. Getting to individual beams under a summer house to perform this work can be challenging.
• Limited weight capacity. Wood beams are weak compared to concrete and stone pavers, reducing their capacity to support heavy garden buildings above them.

1st Choice’s ‘No Concrete’ Answer with Timber Subframe Bases

Standard Timber Subframe Base
This is the ideal solution for garden sheds, workshops and garden rooms when the intended site is relatively level or when a base is needed to sit atop and level an existing concrete base; it is also very popular when access to the property is restricted or when people wish to avoid the disruption of concrete base construction.

A sturdy frame is constructed using 100mm x 47mm structurally graded C24 spruce, which has been subjected to an enhanced pressure treatment process to enhance its strength.

To increase rigidity, cross members are placed at centres between 35cm and 42cm (14” and 16 1/2”) and noggins when the base’s width is greater than 1.5m (5’). The frame is levelled and supported on indestructible recycled plastic ground posts manually driven into the ground.

When the timber subframe is sat atop a concrete base, these plastic posts are not required, and chunky timber feet are used instead when levelling is required.

Heavy Duty Timber Subframe Base
Whilst our standard timber subframe bases are ideal for most situations, sometimes something more robust is called upon. This may be because the building is particularly large or heavy, the plan is to store a large amount of weight within the building, or simply because the ground on which the base is situated has more than a minor slope.

Whatever the reason, our installation team will upgrade the standard specification by upgrading the fixings to coach screws, digging out each post and concreting these into the ground and, where necessary, fitting diagonal braces to add rigidity to the joint between the ground post and the rame (when the base is elevated out of the ground). A wise upgrade when ordering a log cabin or other larger building; please ask our sales advisors for guidance if you need more clarification.

You can find more details here.

Consider these advantages and disadvantages When deciding on a base for your garden room. Manufacturers will usually advise you which base type works best with their items.

Step-by-Step Guide to Building a Garden Building Base

Some homeowners use professionals to construct garden-building bases. However, you can do it yourself if you feel brave.

Getting this process right can be challenging, so follow the instructions in this guide. Deviating from them could risk your summer house (or any other garden building you place on top).

Clearing and preparing the site

The first step is to clear and prepare the site for the installation. Doing this correctly increases the likelihood of installing a durable base.

Start with area clearance. Remove anything that might get in the way of construction. For example, ensure you eliminate:

• Grass
• Weeds
• Shrubbery
• Rocks
• Bricks
• Garden waste
• Compost

The site should be free from anything other than soil. If you want your summer house to sit on your lawn, be careful how much grass you remove. Taking away too much could jeopardise your aesthetic.

Once you clear the area, measure the base’s outline. Marking where it will go shows its footprint on your garden.

Most DIYers do this using a combination of string and stakes. You can also use paint to mark the area, but you should leave it to dry to prevent damaging the base materials.

Always use a measuring tape to mark the shape of the area for the base. Remember to factor in the shape of your summer house when choosing a footprint. Most units are square or rectangular, but some are hexagonal or octagonal, making base construction more complex.

Ground Levelling

The next step is to level the exposed land. Making it flat makes it more straightforward to construct the base.

Most land is not perfectly level, so you should assess the slope. Identifying little peaks and dips helps you determine whether you need complete levelling.

The land may be bumpy but otherwise level. Other patches are on large slopes and are more challenging to level.

Consider building your summer house elsewhere if the land has a significant gradient. Removing slopes requires substantial excavation work, and you may need to install additional retaining walls.

Levelling slopes for garden buildings requires adding and removing soil. Unless the slope is steep, ensure the levelled area represents the average height of the surroundings.

Use a shovel or rake to distribute the soil evenly over the land for small jobs. Removing soil in some areas and depositing it in others can create a more level surface.

Hire machinery for larger jobs. Diggers and tractors can level patches of land using various scoops and attachments.

Ground levelling is a complex task that may take a long time. Be patient with it. If you aren’t happy with the levelling for one day, go back to it the next and try again with fresh eyes.

During levelling, ensure the soil remains inside your marked perimeter. If possible, avoid taking soil from other areas.

Lastly, ensure the levelling doesn’t adversely affect drainage near the site. Don’t level an area of land if it slopes towards an existing building.

When preparing land, see where the water runs. Check it flows away from existing structures into proper drainage channels.

Skilled garden building base installers can level land to slightly slope in the preferred direction. However, you should only do this if you have the skills and the need.

Weed Membrane Installation

Laying a weed membrane might be necessary in some areas. Putting it down prevents persistent weeds from pushing through the soil and damaging the sub-base.

Do not use standard weed membranes. They may not be strong enough to protect your garden building. Use products for summer houses specifically, fitting them over the edges of the base area with the supplied fittings.

Allow The Soil To Compact

Once you finish levelling, leave time for the soil to compact. Letting it squash reduces air pockets and makes it more stable.

Unfortunately, passive soil compaction can take weeks or months. Therefore, professionals use various compaction tools to work faster. These press down into the soil repeatedly, hammering it into place.

Compaction tools instantly reveal differential densities in your soil base. If you notice any developing, add more soil, rake over, and keep compacting.

When compacting, work methodically. Begin in one corner and move in lines until you cover the marked area. Keep going until the soil stops moving.

If you don’t have any compaction tools, hire them from a local builder’s yard or equipment merchant. Compacting land to an acceptable density shouldn’t take at most a day.

Add the base material

Once you prep your garden base, the next stage is to add the base materials. Here, we list all three base materials and how to install them.

Concrete Base

Concrete base installation begins with concrete preparation. You can use ready-mix concrete (prepared in a mixer) or bagged concrete for a smaller garden building.

You will also need:

• A spirit level
• Edging boards
• Crushed rock sub-base
• Mixing tools
• Wheelbarrow
• Shovel
• Goggles and gloves

Concrete bases sometimes require excavation (not just land levelling). Therefore, you may need to dig into the ground.

Most experts recommend going down 100mm (around 5 inches) if you have soggy soil in your area or want to place a heavy building on the base. Once the excavation is complete, you can add the aggregate. It will serve as drainage for the base, preventing rising water from causing flooding or other damage.

You may also need to engage in formwork for large concrete base installations. Edging boards line the base’s boundary and contain the concrete while it sets.

After finishing these preparations, it is time for the concrete. Mix this according to the manufacturer’s instructions (concrete mixing varies significantly by brand).

Once mixed, you must pour the concrete quickly. Leaving it too long could cause it to set before it enters the base.

Pour the concrete onto the marked base area. You will notice it spreading out to fill the space. (It won’t spread out if it is too thick, so you should prepare a new batch).

For large bases, use a concrete pump. These pumps push heavy material from a truck to the nozzle, reducing reliance on wheelbarrows and other makeshift solutions.

Once you pour the concrete, level it to create a flat surface. Most DIYers use a screed, a simple handheld device. Rake it over to ensure the concrete is level with your edging boards (if you’re using them).

Ideally, the concrete should slope slightly away from your main buildings for proper drainage. A perfectly flat surface could result in water pooling or surface runoff in the wrong direction.

The final step is finishing and curing. Concrete requires time to set correctly.

Most products take 24 to 48 hours to dry. However, some concretes may require up to 28 days before they reach full strength.

Some professionals place summer houses atop concrete bases during the curing process. This approach is risky since the weight of the building could leave impressions on the concrete. Therefore, always follow the manufacturer’s instructions. Wait to start using a concrete base until it is ready.

Paving Slab Base

Adding a paving slab base requires a different approach. The first step, as with concrete, is to collect your materials. You will need:

• Paving slabs
• Crushed rock
• Sharp sand
• Spirit level
• Rubber mallet
• Mortar-like compound

Once you have the materials, the first step is to add the sub-base. The process for this step is almost identical to concrete. You start by excavating the ground to a depth of 100mm and filling it with suitable hardcore for the weight and size of the summer house.

Next, add the sharp sand. It provides a soft, even bedding material for the pavers. (Concrete doesn’t require this step because it can fill the gaps around the aggregate).

After that, you can lay the slabs. Professionals usually begin in one corner and work their way around.

When laying each slab:

• Check it is even with the spirit level
• Ensure it doesn’t wobble from side to side
• Check it fits the overall pattern or effect you want to create

If a slab isn’t level, use a rubber mallet to encourage it into the proper position. If necessary, add more sharp sand underneath or around the slab to support it.

The last step is “jointing the slabs, ” filling the gaps between them with a mix, like mortar. Don’t make the compound yourself. Instead, use the one supplied by the vendor.

Sometimes, slabs must be cut using a slab breaker to ensure they are in the proper shape. These machines use diamond-edged cutters to hew through the rock and break it into smaller chunks.

If you feel uncomfortable with this step, get a professional to pre-cut slabs according to your base plan. This approach reduces risks and increases the likelihood of favourable results.

Timber Sub-Frame Bases

Timber sub-frame bases are the simplest to install and require the least specialist equipment. To create a timber sub-frame base, you will need:

• Suitable pressure-treated timber beams (for your building’s weight)
• Concrete foundation blocks
• Screws
• Drill
• Spirit level
• Saw
• Sharp sand

Check with a timber merchant if you need to find out whether the timber suits your summer house. Experts can advise on the best outdoor wooden beams to use.

The first step in installing the timber sub-frame base is to place the concrete blocks or pads. If you don’t have any, you must lower them into the ground and space them appropriately for the building’s weight. Check that they are level with your spirit level, and add sharp sand if they are not.

Next, cut and assemble the timber beams (unless you bought pre-cut wood). Use your saw (or other wood-cutting tool) to cut pieces of wood into their designed lengths. Use the drill and screws to attach the pieces of wood according to your plan.

Lastly, the completed foundation will be fitted to the concrete pads. Use L-shaped metal brackets and fix them with concrete-specific screws.

Who Should Build the Base?

When it comes to building a base for your summer house, you have two options:

• DIY with help from friends.
• Professional “no-nonsense” experts for peace of mind

Building the base yourself costs less upfront, but the risks are higher. While your friends might seem competent, mistakes they make today could cost you later.

People who should build bases for their summer houses are those with significant building or construction experience. If you have done work like this before, nothing should stop you from applying the same principles to your property.

All three bases discussed above require expert construction knowledge. However, concrete versions are arguably the most complex since they require specialist equipment and an understanding of levelling and curing.

If you already have concrete pillars or pads (or supporting brickwork), adding a timber subbase might be something you can do at home as a keen DIYer. But you must still follow the layout plans carefully and use the proper beams (heat—and pressure-treated).

If you haven’t previously constructed a summer house base, a professional “no-nonsense” approach may be better. This approach costs more upfront but may save you money in the long run if you make mistakes.

For example, professionals bring their expertise to the construction project. Unlike DIYers, they have years of experience delivering similar projects and understand every aspect of site preparation.

Better still, they can get the work done faster. Professionals spend less time on simple jobs and move swiftly to complete projects.

Also, you are more likely to get higher-quality results using experts than a friend. Professionals must stand by their work and deliver quality results to get paid. Someone you know in the village may operate to different standards.

Lastly, using professions is considerably safer. Experts lift paving slabs and pour concrete every day, so they understand the risks. Amateurs may not. Possible injuries from doing it yourself include splinters, trips and falls, and back, neck, hand, and toe injuries.

How Can First Choice Help You?

We at 1st Choice specialise in offering an extensive collection of quality timber, concrete and metal buildings, so you can be assured that you will find your ideal building with minimal fuss. There are occasions, however, when other specialists are required to complete your project, and our years of experience in this field mean that we have built up many valuable connections with reliable tradespeople whom we have put forward here for your consideration.

Whilst the individual tradespeople are independent of us (thus keeping the pricing as low as possible), we are happy to liaise with them to make arrangements on your behalf. We, therefore, take a deposit, which is passed along to them with your order. They will collect the outstanding balance upon work completion and leave you with an invoice for your records.

Prices quoted presume a suitable, accessible work site within 50 miles of our display area near Woking. If your site is further afield or access is poor, the standard quoted prices may be subject to an additional charge. You can find more details here.

Tips for Maintaining and Repairing Garden Building Bases

Garden-building bases are usually quite robust. However, they still require regular maintenance.

But what do you need to do? Let’s find out.

Regular inspections

Proper maintenance begins with regular inspections. Checking your base for damage prevents minor issues from becoming more serious.

During inspections, you should look for the following signs of damage or disrepair:

• Damp patches that remain even in warm weather or after storm waters subside. (Damp areas will appear darker on concrete and wood).
• Beams or concrete pads/blocks that wobble or move when you touch them
• Cracks in the base
• Rot in wooden base materials
• Bases at a different angle from when you installed them. (Bases can sometimes move due to ground movement or subsidence).
• Soil pushing up against the base or the bottom of the summer house
• Cracks or breaks in the jointing material on paver slab bases
• Uneven paver slabs
• Evidence of excessive aggregate or sand washing out from under the base (usually in the direction of draining water)

Most inspections will not reveal any issues with your base if appropriately constructed. However, it is worth watching because problems can be costly if left to fester.

Repairing cracks or damage

Cracks in summer house bases can be cause for concern. However, the action you take should reflect the severity of the issue.

Concrete

Minor hairline cracks aren’t worth worrying about in concrete. Just make a note of them and take action if they get worse.

However, cracks less than 6mm in concrete (about a quarter of an inch) require filling. Leaving them can lead to freeze-thaw weathering, where ice freezes inside them and expands, forcing them wider apart. Over time, this process can lead to structural damage.

To repair a concrete crack, clean the immediate area around it, such as leaves, soil or twigs. Next, use a concrete filler. Ensure you insert the filler into the crack. Filling it up completely prevents dangerous water ingress (leading to freeze-thaw weathering described above).

Most professionals recommend applying flexible sealants to the repaired area when it dries. These can expand and contract with the underlying crack and filler, waterproofing the fix.

Paving Slab

Paving slab bases can also crack. As with concrete bases, the fix you implement depends on the severity of the damage.

You can fix uneven slabs by adding or removing sand underneath individual paves. However, accessing them may require moving your summer house off its platform.

For heavily damaged pavers, replace them with new ones and re-joint them. With proper jointing, you can also turn a single cracked paver into two slabs. Just ensure it isn’t load-bearing.

If you notice multiple cracks in your paving slab base, it might indicate ground movement or subsidence. Unfortunately, this situation might require a complete reinstall on stable land.

Timber Sub-Frame Bases

Finally, timber sub-frame bases can crack in some situations. Again, you will need to repair non-superficial damage.

If you notice a minor crack on a beam, try sanding it to see how deep it runs. Superficial cracks can look worse than they are.

If the crack goes deeper, replace the beam. Unscrew it from the rest of the structure and add a new piece of wood that fits your specifications.

Sometimes, cracks can occur because of rot or insect damage. If this happens, check for evidence of dampness and insect damage. Also, check you treated the beams appropriately before installing them. Most insects will ignore wooden beams coated in preservatives.

Preventing water damage

Preventing water damage involves stopping it from reaching your base in the first place. Therefore, consider this from the start of the construction process.

The best way to prevent water damage is to arrange the base so it slopes in one direction away from your buildings. A slight slope allows water to run off while providing a sturdy base. As discussed above, achieving a shallow angle while providing a sturdy base for your summer house is challenging, which is why so many homeowners use professionals.

You can also prevent water damage by implementing proper drainage around your structure. Using an appropriate sub base, drain lines, and gullies lets your summer house rid itself of excess water during downpours. During your inspections, check the drainage leads into the surrounding land and waterways. Slowing the runoff can help prevent flooding and stop water from filling the excavated area.

Finally, consider the materials you use. Most professionals use waterproof concrete for the foundations. These concrete mixes have additives that prevent porous holes from forming during the curing process. Waterproofing also prevents dampness from spreading through the material, even with standing water.

Treating wood also prevents water damage. Do this every couple of years or so.

Conclusion

Reading this guide, you should better understand the value of a good base for your summer house. It is essential to ensure the structure above it remains stable, level, and damp-free.

However, getting it right requires knowing what you are doing. If you need more clarification, use professionals.

If you are considering building a summer house in your garden, consider the most suitable base. Concrete might be best in some situations, while paving slabs are better in others. Take the weight of your garden building and soil type into account.

What are you waiting for if you still need to start your summer house base project? Get your project off the ground today and build your garden sanctuary.

Frequently Asked Questions (FAQ) Summerhouse Bases