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The Sauna project

Having first seen the WW2 Air Raid Shelter in my Garden, the idea was born to build a Sauna into this unique space.


That was back in summer 2002. Since then I collected information on Sauna DIY and compared Sauna merchants and builders, using the internet also to order prospectuses, but nothing real developed, as other projects took priority. However now the time is right, and the project can take shape. I build these pages and took the pictures at the same time while building the Sauna.


They are designed for you not only to see how the project evolved, but also to give you some ideas, as you may want to do something similar. The project was completed in 2004.

Please enjoy. I hope you find it informative and helpful.

On these pages, nothing is sponsored and you can view all sections for free. All recommendations are based on my own experiences and views. Should you whish to reproduce part of these pages, pictures or illustrations, or quote sections or myself, you are kindly requested to receive my prior consent as I exercise my copyrights.

Axel Thill, build and written in April 2004

Part 1 

All about... Preparations

The Air Raid Shelter

The Air Raid Shelter is a free standing building, with 14 inch thick walls and a 10 inch thick concrete roof-plate. Above picture was taken after completion.

The first pictures above give you a idea of how that place looked like on the inside. All shelves had to be removed, then the old rotten window at the end was closed, now only a small air inlet remains. In a next step the floor was levelled in preparation of the tiling. In the 3rd picture the area is now tiled, but not yet grouted.

Note that in such a small space I took the pictures with a super wide angle, thus some distortion  occurred. The tiles are actually square 30x30 cm.

Suzi and Tony from

Suzi and Tony, working for AB Lagerholm UK,  became 2 very important persons for my Sauna project.  I looked around in many places, surfed the web, compared all informations and read numerous prospectuses, but they at Finnsauna gave me the best impression, valuable ideas and a lot of help.


Have a look under (previously . If you want to build your Sauna, that is the place to check out.


Special thanks to Suzi, as she is great in drawing plans, and will do so incorporating all the information, crazy ideas and special whishes you may give her. See on the left what she came up with for me.

Lets build it. Soon I will take delivery of all the material needed. The order-list has also been prepared by Suzi, so I do not need to worry that something is missing. All I had to do is measuring the air raid shelter correctly.

The wood from Lagerholm

Lagerholm provided 2 very important woods: for the Sauna interior Spruce panels and "Aspen wood (Abachi)" for the "body-sensitive-area" of the benches and backrests. The picture below is only a small portion, as 160 Spruce Paneling at 2.1m length (2.95 GBP) and 50 Aspen boards at various length were ordered. You can save some money in specifying the approximate length of the Aspen panels (1.6m (6 GBP), 1.8m 2.1m (8.4 GBP) or more), it will have a noticeable impact on your budget.

The prices shown above are 2004 prices...

The wood sourced locally

For framing the walls and building a solid ladder frame for the benches, I sourced (as recommended by Lagerholm) the wood locally. In my region (SW of London) a well stocked merchant is Champion, you can find more details on their website under They are delivering over a wide area.


To save some money, I ordered 2 types of wood in 3 sizes:


Premier Planed  (the nice one you will always see)

Frame Grade (treated)  (the rough one you will never see again)

A word on tools...

I invested for this project in a new tool, a Mitre Saw from Bosch (GCM 10 254mm)


You will not regret to own such power tool, as over 200 pieces of wood will have to be cut to size. And as you do not want to have a visible bad job, specially not on the quite expensive Aspen wood for the benches and backrests, spend some money here.


For a great online shopping experience, I recommend It is a real pleasure to buy online from them. They have a very good and huge catalogue to browse, great bargains, and are very reliable and secure.


Here are some of the other tools, insulation, screws and nails used:

Part 2
All about .... Framing and Paneling

All materials arrived, the Air Raid Shelter is prepared and ready, now the actual work on the Sauna can finally start.

Step 1: framing and insulation

I changed my mind: I do not just recommend to buy a Mitre Saw, IT IS A MUST. Do not start without it. Just the framing, with heavy wood, will make you fall in love with the machine. Framing 4 walls and a ceiling, are "just" 20 horizontal battens, but they also have to be pretty accurate.


I fixed each batten with 4 or 5  screws, depending on the length of the wall.


Have some fun and build your own tools and guides, it will make you life so much easier. See these odd looking but useful pieces and guides:

< ^ This piece of wood helped me to determine horizontally where the screws should be fixed, to have a gap to the floor, and allows to space the screws between 50 and 60cm. No meters needed.



side wall 230cm = 15 cm + 4 x50 cm

back wall 208cm = 14 cm + 3x 60cm 


Also use it to determine vertically the height of the next horizontal batten, so fit the Rockwool firmly, I spaced the gap 57.5 cm (lower batten to next screw 60 cm minus half width of batten), a little less than the Rockwool width of 60 cm. Again, no meters needed, but very accurate.

This little stopper will help you to cut 4 panel pieces with your new Mitre Saw at one time, making sure the "other end" (which is 2m away from you) stays aligned. The whole build was a 1 man show, with no second set of helping hands.

Drill a small hole (4-5mm) in the batten where the screw will pass, this will not reduce the overall strength, but help you to fix the 9cm long f.@%*# - screws to the wall and prevent the batten to split.

Into the box with the screws, spray a little bit of oil or MD40, very little, I guarantee this will also help you to stay mentally balanced after the 50th screw.

Keep the area tidy, have a old but working vacuum cleaner and clean away concrete dust and wood chips after each 2 batten, your new tiling will thank you for it. Keep it straight but do not be surgically critical for levels and accurate distances with this work, it does not matter here, as all will be hidden behind panelling and the Rockwool can easily be squeezed in.

Once all batten are fixed, do not start with the Rockwool fitting, I know its tempting, but now its time to think about all electrical cables (lights, oven, sensor, ventilator etc...)


Always call a professional electrician for advise, be very careful with electrical stuff, you need special high temperatures cables for the lightening.

Step 2: do not forget the Strong Points

This is very important: on the left you can see how I solved the issue of Strong Points for fixing the bench supports, as with up to 3 adults they may need to support ... a lot, over 250kg. Do not rely on the battens, they are for fixing the panelling, and will not be at the same hight as the bench support. And the thin panelling alone does not hold these weights...

The additional horizontal wood was supported vertically (like legs of a table) and has been added to center at a height of ~70 cm, as adding the height of the frame of the bench will then give you a upper sitting height of around 80-82 cm. The lower benches, used as step and sitting, receive similar strong-points, as does the stove, heavily filled with stones.

< left support of backbench

right side support of backbench

left support of sidebench

oven support and left side of backbench

As you can see above, as soon as you started to add the panelling, all Strong Points are invisible. I printed my photos of the structures on a simple black and white printer, and then wrote on the paper the exact distances to floor and wall. 

One of the bigger operations was the installation of the door.


I did not build the door, but bought it ready made from Lagerholm. But you have to secure it in the right location in your Sauna. After some pushing, nailing and the odd screw I had the door finally standing upright and square, and I could lean against it. The surrounding panelling will give it further robustness.

Another odd details while building the batten frame was the air-outlet near the ceiling, where I added a electrical ventilator. This allows ventilation while the sauna is not in use, but the outside weather humid. The Sauna is free standing in the garden. This part will later be covered by the sliding "Shutter" vent. 

Step 3: the Panelling

Then, after many hours of work, after all Rockwool has been squeezed into place, and after the vapour barrier has been fitted, then finally the work with the "nice wood" can start.


I started the paneling with the ceiling, as it will allow me to cut the wood with a higher length error tolerance.

These small "errors" are not critical, as the wall paneling will cover them up. Now the Rockwool and vapour barrier to the walls will be added.


But from now on you need to be more accurate when cutting. 

Try to keep the panels of the ceiling and walls properly aligned, all will start to look quite tidy. See the beading that was added to the corners, they will later also be added to the ceiling. The red cable in preparation for the lightning. And better leave a gap at the bottom over your floor, as humidity could later kreep up and damage the panels.


Your arm may start to hurt, but do not compromise:  8 nails per panel! 

                                         You can not "over fix"

Ups, what cable is coming out there ??   Well, I dreamed enjoying the Sauna while listening to Art Garfunkel's Breakaway, the latest Norah Jones album or a Classical Chillout CD. I could not resist and build in cables for stereo speakers. The player can stay outside the Sauna, the speakers have to endure not much heat, as they are standing on the floor and the high temperatures in a Sauna are high up under the ceiling. 

Part 3
All about .... the Interior

Now that the paneling is done, the construction of the benches and footrests can start, the lights will later be hidden, but first they have to work.

When building the upper and lower benches, you are going to use the good and expensive Aspen wood. Unfortunately not all are in best quality, that's nature, but most of the time they have a good side. You can use them without problem, just make sure the "bad side" is hidden and shows downwards.

<  Here you can see the back bench (upright) and the right support bar, that received a very strong fixing to the wall, behind which are the important strong points


I wanted to make sure that the Sauna room could also be used as a "normal"  room or for storage. Lets hope it will never happen, but health (or new owners) could lead to the closure of the Sauna in the distant future. Thus I try to keep the parts as "movable" as possible. Take this first bench, it is very solid, but can be removed without a screwdriver. Just lift it up.

<  This back bench is 170 cm wide and its depth (50cm) is 5 Aspen panels.

The next feature to solve was that I do not like supporting legs going to the ground, I wanted all to "float" in the room.

Well, no leg used yet, and here is how I solved the fixing of the side bench.

The left picture below shows a small vertical wood that I called the "insurance policy", with 2 functions: first to stop the underlying wood to break where the now invisible long screw was fixed, and secondly, should a leg be needed, here is where it would be attached.

Will it hold the weight? It did on day 2, and I can report it still does on day 4,750 (after 13 years)


The overall "floating" look from above is great 

This bench is 150 cm wide (+50cm back bench, giving a total length of 200cm) and  its depth (60cm) is 6 Aspen panels. Plenty of room for a big person to stretch out.


Another day's work: the lower benches and corner light shades, which also double as corner backrests, giving the room a less cubic feeling.  The same "footless" system for construction is used for the low benches as for the high benches.

These 2 benches, or better say footrests, are 170cm wide and 40cm (4 panels) deep,  and 150cm (110+40) with a depth of 3 Aspen panels (30cm). 

Still all benches can be removed without the need of any tool. Each corner light shade is kept in place by 4 screws, which need removal should a light-bulb break. This allows stacking the benches to temporarily store something else in this new room. This is also the reason why I did not build valances as first planed.

Above how the place looked when we started in April 2004, and on the left what was achieved within 6 weekends of work.

2017 addendum: after 13 years of operations, heating up the Sauna every Sunday in the cold months, and twice a month in summer, the Sauna is still in pristine condition and our evening joy. The only thing I had to change once was the middle light bulb.

Over the years, I received many feedback and questions from DIY enthusiasts, inspire by this report to start their own Sauna project. Feel free to contact me should you have any questions, though the real experts are at the Sauna Shop.

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