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Laying the foundations is the first and extremely important step on a cottage or sauna building site. The foundations of a garden sauna or cottage are literally the basis for everything and are difficult to repair afterwards. Proper foundations ensure that the building withstands time and does not, for example, warp or sink.
Foundation work involves three stages:
- Soil investigation and foundation method selection.
- Foundation design
- Foundation construction
The location of the building and the soil in the area significantly influence the choice of foundation method, so the work always begins with a soil investigation.
This guide provides clear information on selecting the right type of foundations and instructions for building different types of foundations.
👉 Read also why winter delivery is worthwhile and how it affects foundation work.
Soil surveying provides the foundation for selecting the foundations for both the cabin and the garden sauna.
Soil testing provides the basis for choosing the foundations for a cottage or a garden sauna. If the soil composition is unknown, soil testing is the first step towards your dream sauna.
Soil survey have it done by a professional or DIY. The previous owners of the site can also provide valuable information about the soil. The aim of the research is to clarify the soil structure, load capacity and groundwater level.
Each soil behaves differently:
- from the other it flows down quickly,
- others bind moisture,
- most soils freeze hard,
- Others hardly at all.
In Finland, the behaviour of moisture and frost heave pose the most significant risks to foundations. The power of nature is astonishing: frost heave moves soil particles both vertically and horizontally – regardless of the heavy building on top. Therefore, a wrongly chosen or poorly constructed foundation can backfire through settlement of the building or structural damage.
Soil types and their effect on foundation selection.
The most common methods for building a cottage or garden sauna are screw pile, pillar, and light foundations. These are used depending on the soil conditions as follows:
- On soft, loamy soil Is well suited Screw pile foundation.
- To bedrock and moraine is usually chosen traditional pad foundation.
- Uncompacted subsoil such as rock or sand/gravel allow for a lighter foundation method.light foundation).
Consult the table to see which foundation is suitable for which soil type:
| Screw pile foundation | Pillar foundation | |
| Kallio | – | x |
| Gravel/sand | x | x |
| Moraine | x* | x |
| Sand/silt | x | x |
| Savi | x | x |
| Peat slurry | – | – |
Large stones may be present in the moraine that could hinder the installation of screw piles.
Peat, silt, and other organic subsoils must always be removed from beneath foundations.
Based on our experience, the traditional pier foundation is the most common foundation method.
How to choose the right foundations for your cabin or sauna – instructions and costs
The foundation for the sauna or cottage will ultimately be chosen. soil, factors competence and preferences accompanied by. Once the soil structure is known, the final selection can be made, taking other factors into account.
Typically, a screw pile or pier foundation is chosen for building a garden sauna or cabin; if the ground conditions permit, a raft foundation can also be used.
But how do you make the right choice? And how much do foundations cost?
You will soon get answers to these questions, as next you will receive easily understandable information about the three most common basic types of foundations.
Screw pile foundation
Screw pile foundations are a newer alternative to traditional concrete or brick foundations. A screw pile, also known as a ground screw, is a steel pile that is screwed into the ground below the frost line.
There are screw piles hand-wound a lighter model that can be self-installed and a more robust one machine-installable The machine can be rented or purchased with screw piles pre-installed.
Screw piling Does not require significant earthworks Yes, pile driving is also possible in tight and difficult-to-access locations, as well as in damp soil, as long as the length of the screw pile is chosen correctly. The pile must be installed under the router, so that it stays in place.
Screw piles are not suitable for rocky or stony ground., as they are screwed into the ground, with larger stones preventing the installation of the pile. If you still want to choose a screw pile as a foundation method, stones can be removed from the pile locations with an excavator and replaced with more level soil. However, this will likely be more expensive than, for example, a pillar foundation.
Suitability
+ Sandy soil, loam, moraine
+ Suitable for all Ehta's garden saunas, sauna cottages and cottages.
– Not suitable for rocky or stony soil.
Construction
+ Doesn't leave tracks in the yard.
Can also be installed in winter.
+ Quick installation method – no drying time.
Specifically, the manually installed model is affordable.
– In some cases, it can be more expensive than a pile foundation when installed by a professional.
Options and costs:
- You can find self-installing hand-screw ground screws in all hardware stores.
- Pile prices: £20-£60/person.
(Remember to choose a sufficiently long post that reaches below the frost line!)
- Pile prices: £20-£60/person.
- Screw piles that are installed by machine are usually installed by a professional. (e.g. Stop digging works throughout Finland.
- Price of a pile with installation included: €200–300 per couple (The location of the property can significantly affect the cost!)
- DIY machine installation
- Pile prices: €30-80 per item;
- Machine rental, e.g. from a hardware store: 80-150€/day.
2. Pile foundation
Pile foundations are the most common method for building holiday homes and garden outbuildings. Extensive groundwork is not required for piles, and installation is generally straightforward when the foundation area is small.
Building a sauna on pillars allows for good ventilation beneath the structure. This is a significant advantage for moisture management in sauna buildings.
Pillar foundation requires frost protection even if the soil can freeze. If frost insulation is done carefully, a pile foundation is an excellent option even in frost-prone soil.
When building on rock or sandy soil, frost insulation is not required. On rock, piles can also be founded directly onto the rock, and separate concrete footings are not needed to support the foundations.
With over 1600 garden sauna experiences, most of our customers find that the BCE pillar, shown in the image below for example, is the easiest way to build the foundations for a garden sauna or sauna cabin.
Suitability
Suitable for frost insulation with all soil types. (Organic matter must be removed from beneath and replaced with gravel/sand.)
+ An exceptionally easy solution for unfrozen ground and rock foundations.
Construction
Cheaper if made yourself.
Good load-bearing capacity, sturdy and durable
– Requires ground excavation and frost insulation.
– Excavators are usually needed for groundwork, which increases costs.
Options and costs:
- Ready foundation pillar BCE
- The BCE pillar is a ready-made, downwards-tapering concrete pillar that does not require a separate foundation.
- On top of the pillar there is an adjustable pillar shoe.
- Price is £60–70 per litre
- Reinforced concrete column
- A block pillar is formed from a reinforced concrete footing and pillar blocks placed on top of it. The hollow centre of the pillar blocks is reinforced and filled with concrete. An adjustable column shoe can be added to the block pillar during casting.
- Price 30–40 € per batch
- Cast-in-place concrete foundation and column
- Pillars can also be cast entirely from concrete on site. In this case, a formwork is made for the footing and the pillar, which is reinforced and filled with concrete. An adjustable pillar shoe can be installed on top of the pillar.
- Price 30–40 € per batch
The total costs must also take into account potential excavator work, crushed stone, and frost insulation.
Instructions for foundation dimensioning:
Foundations must always be constructed precisely according to the building's measurements. When foundations are made for a pre-fabricated cabin or sauna, particular attention must be paid to dimensional accuracy.
Prefabricated buildings are made precisely to measurements, and the same is required of the foundations. Otherwise, it simply won't be possible to place the sauna or cabin onto the foundations.
- The longitudinal tolerance in measurement may be no more than ± 20 mm and the vertical tolerance may be no more than ± 5 mm.
- If adjustable foundation piers are used, they make it easy to adjust the final centimetres to the same height.
- The squareness of the foundations is checked Cross-channel once it has been confirmed that the opposite sides of the foundation are of equal length, it is then measured to ensure that both diagonal measurements* are the same. When all these measurements match, the corners of the foundation are square, i.e. At a 90-degree angle.
Diagonal means the measurement from corner to corner of a building.
Tip: When constructing foundations, also consider a drainage pipe for rainwater if there is a need for one.
Here's how to build the foundations for a cabin or garden sauna yourself
Often, cottage foundations are ordered ready-made, which is an easy and reliable choice. Foundations can also be made yourself, especially if you have previous construction experience.
When it comes to prefabricated houses and cottages, special care must be taken to ensure precise dimensions.
Below you will find instructions on how to carry out the two most common foundation methods yourself.
Build your own pile foundation – video and step-by-step instructions:
- Mark the building's location and the level on stakes and plumb lines. A spirit level and a laser are also good aids for this.
- The topsoil will be excavated. at a depth of at least 50 cm. We recommend an excavator for this stage, but if the building is small and the soil is not too challenging, it can be done with a spade.
- Lay a filter fabric on the base. Geotextile is placed between the sub-base and the fill material, so that the soil components do not mix together over time.
- Put coarse aggregate Use gravel to fill the void left by the removed soil, in layers of approximately 15 cm. Use a spade, rake, and a piece of board about 1.5 metres long to help level it.
Smooth and summarise Please check. A hand tamper may be sufficient for compacting a small building, but we generally recommend renting maraca, so that the soil is guaranteed to compact sufficiently.(Enquire about rentals, for example, at hardware stores. The price is usually €40-60 / day).
Ensure the ground is level using a water jet or laser.
Lay the insulation boards The entire construction industry extends to approximately 1.5 m outside the sides of buildings. The thickness of the frost insulation is 10–20 cm, depending on the climatic conditions of the construction site.
- Add 10–15 cm of crushed stone on top of the frost insulation.. Compact carefully to avoid breaking the discs (light tamping or hand compaction is sufficient).
- Do another interest rate check. and make sure all the pillar locations are on the same level. Use laser Taiwan spirit level Yes Sticking plaster. The finishing of the ground surface must be precise!
If you are unsure about the sufficient evenness of the ground surface, use height-adjustable foundation pillars, so that the height can still be fine-tuned afterwards. - Lay the foundations and pillars yourself or install pre-cast foundation piles. Ensure there is adequate ventilation space between the finished building and the ground, usually 20 cm.
The size, height, and number of pillars are determined From the foundation measurement drawing provided by Ethan. It provides ready, clear instructions for building foundations once the soil structure is known.
Make your own screw pile foundation – video and step-by-step instructions:
- Mark the building's location mark out the locations of screw piles in the ground, for example with stakes or spray paint. The number of piles depends on the size and weight of the building. If you purchase a building from Ehto, we will deliver foundation drawings that show the correct number and exact placement of the piles.
- Ensure dimensional accuracy. Remember to also check the diagonal measurements (linking to the previous one) to ensure the corners are square.
- Remove topsoil, such as soil and peat at the pile locations. If necessary, place filter fabric and a thin layer of crushed stone in its place. If the ground is loose, this makes it easier to install the pile.
- Install the piles either manually or with a dedicated machine.
- This is how a screw pile foundation is made by hand.
Hand assembly is only recommended for small structures and on easy, stone-free ground.
Instructions Position the installation arm through the top holes of the post. Two people turn the arm around while simultaneously pressing the post downwards. Check for verticality with a spirit level during installation. Continue until the post is below the frost line. (Check the frost line for your local area!) - This is how a screw pile foundation is made with a machine.
Screw pile machine hire is £80/day.
Making a screw pile foundation with a machine is faster and easier than manual installation. Furthermore, there's better torque if stones obstruct the pile's path. However, screw piles cannot be installed even with a machine in soil containing large stones.
Instructions First, familiarise yourself with the machine's operating and safety instructions. Start the machine, place the pile in the machine's chuck and press it in while drilling. Check its verticality with a spirit level intermittently. Continue until the pile is below the frost line.
- This is how a screw pile foundation is made by hand.
- Check the interest rates, so that the tops of the piles are level. You can also use adjustable pile shoes for fine-tuning the last few centimetres.
The K-rauta video on terrace screw pile foundations works just as well. to establish a pigsty with hand-installed screw piles.
The video from Paalupiste gives a good overview of different types of screw piles, their installation, and their applications.
Detailed instructions and images for building foundations
- Do you need help, more detailed instructions, or additional information regarding the foundations for a garden sauna?
- Are you interested in purchasing a sauna or another prefabricated building?
Ehta is a company that manufactures finished saunas and cottages from Finnish log. Ehta is particularly known for its good value for money and warm, knowledgeable customer service.
We have enablers and designers in our company – not salespeople.
