NFU Mutual Smallholding Insurance

Author Topic: Building a Cellar  (Read 5765 times)

oor wullie

  • Joined Jun 2012
  • Strathnairn
Building a Cellar
« on: June 03, 2015, 01:49:21 pm »
I have always fancied having a cellar, it would be great to have a cool dark space to store the tattie harvest, jam, wine and assorted ‘stuff’.   
Building a cellar under the house would have cost an astronomical amount of money and just wasn’t an option so I decided to build a standalone cellar a short distance away from the house.  I found it difficult to find much information about how to build a cellar.  Searching on the internet tends to bring up two slightly different types of cellar – 1 very fancy wine cellars that can be installed in or under your house which are installed by professionals or 2 – survivalist shelters which are for stocking up with tins of food and ammunition in preparation for the day that the government comes to get you (usually American based information!), neither of which is quite what I was wanting.  There must be good knowledge somewhere about building root cellars and ice houses but I suspect that the people who successfully built these are either not on the internet or lived 150 years ago and so are long dead.
Here then is an account of how I built a cellar for anyone that is interested.  It will probably follow as a series of posts on this thread as I get round to writing it and to avoid a massive post.

I am not a structural engineer and a real engineer might be horrified by some of what follows!

Unfortunately I was a bit lax at taking photos of the process so there are not as many as there should be.

Overview.
Basically I dug a hole, built a concrete tunnel in the hole then backfilled earth over it so about half the cellar is below ground level and half above.  The bit above ground is insulated with a thick layer of soil and so appears as a grassy mound with a door in it.  Not too unlike a hobbit house.
Voss Electric Fence

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #1 on: June 03, 2015, 01:53:58 pm »
Step 1.  Site.

First concern will be drainage.  Where is the water table?  If you dig into the water table your hole will fill with water, in theory you could make a totally waterproof cellar to keep the water out but that is getting a bit too technical for me.  Ideally you need to be able to dig a suitable depth without reaching the water table – bearing in mind that in winter it might be higher than in summer. 
You are making a hole in the ground and it will naturally fill up with water which needs to be drained somehow.  If you have a sandy soil it might drain itself, if not the best thing is to build on a slope so you can have a drain coming out of the cellar at floor level. 

Ideally it should be on a north facing slope to avoid the strongest heat from the sun.

Step 2.  Excavation
 Work out how big a cellar you want and dig a hole that is a bit bigger.  When building the walls you need to be able to get at them from the outside so if you are building a cellar that is 3m wide you probably want a hole that is 4m wide to give enough working room.  Depth will depend on how much of the cellar you want underground (which may be determined by how easily you can drain it).  I dug about a meter deep before giving up as the subsoil I was digging through was as hard as concrete and my digger was struggling to scratch any deeper.  I dug a trench out of the front of the cellar going downhill which was fitted with a drainage pipe and backfilled.

Step 3. Foundations.
I roughly shuttered and poured a ring of concrete around the bottom of the hole where the walls would go.  Seeing as the ground was so hard I didn’t make the foundations that big.  Basically a strip of concrete about 15-20cm thick and 30cm wide.  I had some spare steel rebar lying about so that went into the concrete to give it a bit more strength.  Short lengths of rebar were left sticking up out of the foundations to reinforce the bit where the poured concrete of the walls would join the foundations.

Step 4 . End Walls
The back wall of the cellar was built with concrete blocks (laid on their side so the wall was 200mm thick).
The front wall was similarly built with blocks but had to include a doorway and a sump for the stairs down into the cellar.  The diagram below shows the layout.
The outside of the walls was painted with a tanking slurry to waterproof them in-case water started seeping through.

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #2 on: June 03, 2015, 02:20:33 pm »
Step 5. Shuttering.

In order to pour a concrete arch you need to shutter the tunnel shape and make sure it is properly supported, this is probably the hardest and most critical thing to get right.

A length of steel supported some old strainer posts made a strong ridgeline.
Blue plastic pipe was cut to length and bent to make the arch shape.  A couple more horizontal lengths of wood were used to hold the sides of the tunnel  in the right shape.  With hindsight another 2 horizontal supports would have been better as the sides bowed in with the weight of the concrete on them.  The first photo shows the supporting framework inside the shuttering

The ribs of the tunnel were sheeted with a combination of 3mm ply and hardboard.  The ply worked well but the hardboard struggled to hold its shape (but it was cheaper).
As I had no confidence in the concrete sticking to vertical plywood I covered the whole thing with expanded metal lath (the stuff that is used as a base for plastering onto walls).  It was just draped over the shuttering as in the third picture.

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #3 on: June 03, 2015, 04:58:50 pm »
Step 6 – The eggshell

I had no confidence at all that the shuttering would support the 12-15 tons of concrete that would be needed to create the tunnel so the first stage was to create a thin eggshell of mortar which would dry to give enough strength to hold the main layer of concrete.
I used mortar (ie cement and sand (no crushed rock)) as it needed to be fine enough to be pushed into the metal lath so it would not fall off, the bits of gravel in concrete would stop it penetrating the lath.  For this critical stage I used hi-strength cement (white cement which has a higher compressive strength than normal cement) and added fibres to give it further strength.  This was plastered over the shuttered surface to a depth of about 25mm.  Even this thin layer required about 2 tons of mortar which caused some of the shuttering to bow in a bit but by this stage it was too late to do much about it.  You can see on the second photo where the nice curved arch shape has sagged in.

All mortar was mixed by hand and carefully applied with a trowel leaving the surface rough so the next layer had something to bond to.

After leaving it to cure for a day or 2 I gingerly climbed onto of it and found it strong enough to take my weight.

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #4 on: June 03, 2015, 05:10:42 pm »
Step 7 – The main shell

After the ‘eggshell’ had cured properly it was all covered with rebar mesh.  I used 6mm as it was easiest to work with (and bend it over the arch shape).  Thicker re-bar would help support the wet concrete but would be harder to bend into shape.
Next was to cover everything with 150mm of concrete, ideally this should be done in a day to avoid joins between concrete which could become weak points.  Realistically you would have to be braver than me to have a concrete truck dump 8m³ of concrete on-top of your cellar in 20mins (or however long it takes to unload a truck) - you would need to have ordered just the right consistency for it to stick but not slump on the walls, be supremely confident that your structure could take all that weight at once and have a lot of help to be able to get it in place before it cured.  So I did it all by hand with one or 2 helpers whenever I could find someone stupid enough to agree to help.  This involved a lot of work mixing, wheelbarrowing  to the edge of the hole, bucketing into the hole then applying with a trowel.  About a week of backbreaking work.  You need some really good friends for this!

Step 8 – Backfill

I had a load of spare sheets of Kingspan insulation so fixed them on the outside of the cellar to give it a bit extra insulation and covered everything with a sheet of plastic.  All of the soil excavated from the hole was then heaped back ontop, packed down and had grass seed planted on it.

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #5 on: June 03, 2015, 08:27:59 pm »
Step 9 – bits and bobs

Steps were built going down into the cellar and an inner door and an outer door fitted.  The floor of the cellar was bare earth which was always damp (small puddles form at the edges) so it was covered with gravel which allows water to drain but keeps everything above the wet level.

The inside of the concrete could make things a bit dusty so the inside of the cellar was painted white.

Some shelving has gone in and more will get built when I get a chance.

oor wullie

  • Joined Jun 2012
  • Strathnairn
Re: Building a Cellar
« Reply #6 on: June 03, 2015, 08:44:28 pm »
Step 10 – ventilation

After putting the shelving in mould started growing on all the wood.  On reflection the cause is probably due to a lack of airflow through the cellar and I should have put in a pair of ventilation pipes through the roof, one starting at floor level and the other at ceiling level to allow fresh air to circulate as it rises.  A pair of 100mm pipes going straight up through the roof would probably have been the best plan.    So really this shouldn't be step 10 but should have been included before pouring any of the concrete.  Oops.

Unfortunately the steel in the concrete made me reluctant to try drilling through it so I have drilled some horizontal holes through the back wall and inserted some 35mm blue pipe.  I don’t think this will provide enough ventilation but time will tell.  If I need to drill bigger holes I will need to get a much bigger drill to drill through that much concrete!

The cellar is currently at 8 degrees, although given that over the last 8 months we have only had 2 or 3 days below 0C and 2 or 3 days above 10C (come on summer, where are you?) it has not really been tested with hot or cold weather.
Humidity is currently at 97% which I think is too high.  Improving the ventilation would probably help this and I also wonder if I should concrete over the floor as the wet earth will be contributing a bit to this humidity.

I haven't had anything stored in it for any length of time yet so can't say for sure how well it 'works'.  Hopefully this years tattie crop will be big enough to need storing for the whole year!

If anyone has any spare cases of 1st growth Bordeaux that they would like to donate that we could use to trial the cellar with then please get in touch.     

pgkevet

  • Joined Jul 2011
Re: Building a Cellar
« Reply #7 on: June 03, 2015, 10:18:27 pm »
It's very reminiscent of those ex ww2 concrete air-raid shelters the RAF had when i was a kid.. except they had a large square chimney/vent at the end opposite the door. They were also prone to damp.. excellent for growing mushrooms and one which did fill with water was a great source of frogs for us children.

Ventilation will help but i suspect you're going to have a condensation problem too....



chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Building a Cellar
« Reply #8 on: June 04, 2015, 05:23:36 am »
We have a vaulted cellar which is kept completely dry with a dehumidifier. Not necessary to run it continuously, just a few hours every night.

pgkevet

  • Joined Jul 2011
Re: Building a Cellar
« Reply #9 on: June 04, 2015, 01:18:55 pm »
..some inspiration for you...

If memory serves the catal roof method requires a watery plaster like morter and very dry bricks,,

https://www.youtube.com/watch?v=CiEQBboDE7s

Q

  • Joined Apr 2013
Re: Building a Cellar
« Reply #10 on: June 04, 2015, 05:32:16 pm »
..some inspiration for you...

If memory serves the catal roof method requires a watery plaster like morter and very dry bricks,,

https://www.youtube.com/watch?v=CiEQBboDE7s
Thats amazing to watch
If you cant beat 'em then at least bugger 'em about a bit. :innocent:

devonlady

  • Joined Aug 2014
Re: Building a Cellar
« Reply #11 on: June 06, 2015, 06:54:41 am »
Oor Wullie, you could make a good living building Hobbit holes! Was it very expensive to build? And what is "shuttering"?

pgkevet

  • Joined Jul 2011
Re: Building a Cellar
« Reply #12 on: June 06, 2015, 02:54:36 pm »
Shuttering is the form-work that concrete is poured into to cast. Typically a simple parallel row of stiakes supporting cheap 'shuttering' plywood. For more structural formworks such as vertical pillars, crossbeams and the like you'ld need heavier duty shuttering with reinforcng bars (rebar) or cages of rebar.

Basic building materials are relatively cheap.. it's the labour and/or hire of mechanisation that is the greater cost. except for insulation and timber. Decent thick sheets of Kingspan (dense foam) run about £25-30 and you can get through a  lot if it's used under floor as well as walls and ceilings.

The troubles come when you really engineer these things to be damp and condensation-rpoof.. double walls with cavity insulation tied through damp membranes to isolate the middle 'pod' and a thorough peripheral drainage to a deep soakaway

devonlady

  • Joined Aug 2014
Re: Building a Cellar
« Reply #13 on: June 06, 2015, 05:20:10 pm »
So, a sort of "mould" .

Marches Farmer

  • Joined Dec 2012
  • Herefordshire
Re: Building a Cellar
« Reply #14 on: June 06, 2015, 06:01:14 pm »
We have a cellar under the house, which was built around 1560.  It's about 2.4 metres deep and has a 4 metre deep well on one side.  It floods to around 30cm in a really wet Winter but drains away through a drain in the corner (no idea where that goes).  The only ventilation is through the gaps around the (badly fitting) access door but there have never been problems with mould or condensation.  Is your concrete still drying out?  This can take months, depending on the weather.  "Our" newts really appreciate the ground heat exchange effect in a wet Winter as they swim around in a warm(ish) pool.  The floor is just bricks (no mortar) which aids drying.

 

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