Foundations

[Mr Coeur de Lion]

Hi all,

I have a little barn across the road from me that I am intending to convert into a little two bedroom home, as and when my finances allow.  The first thing I need to do is to get some cement foundations laid down, as I will be blocking in the barn with parpaing in order to chaux it so that it looks like the other houses in the street. 

I am planning on foundations about 400mm wide and 600mm deep with rebar rods.  The ground is straight rock (it is built against a rock face), but it is that chalky white rock that is so prevelant in the Loire region.  Does anyone feel that these foundations would be suitable?  My budget is extremely limited, so I can't afford any engineers, and it is only a small building.  The front of the house is 3m high leading back to the rockface at 6m high.

Regards,

Lynda

[BIG MAC]

Insufficient information to give a meaningful response however assuming that you are on limestone then you would want to get down to a formation level which permitted the introduction of a ground beam suitable in width to recieve the proposed wall. I would be surpised if there weren't regulations in respect of footings maybe the Maire could shed light on the situation locally. Building is likely to be very damp if against  a rock face therefore I would allow for full height studded membrane and dry lining if you plan to inhabit the space. Also if it's zones as Agricultural getting the Permis may not be that easy to do either.

All that said Leroys, Pont P etc usually stock what they call (Pardon my spelling) Semmelles de fondation which are pre formed cages in what I take to be standard French sizes. I would allow at least 75mm of concrete cover to all faces of the beam and would wire it to any continuation or returns in the foundation. Its a good idea if you have any plastic sheet lying about to place this in the excavationn prior to putting steel in and placing concrete this will help prevent suction dewatering the mix keeps spoil out  and will give you a steady cure.

[Mr Coeur de Lion]

I have read your reply again, again and again trying to understand your advice, and I think I've got a handle on it.  Not many men would help a woman to understand something so technical without being patronising.  Thank you.

I shall try to find out from the Mairies what the regulations are for footings in the village.  Then I shall buy the required Semelles de fondation and make sure my trenches allow at least 75mm all the way around.  Wiring it together could be interesting as I don't want to remove the large timber frame, but rather lay the parpaing between the posts.  I suppose I could run some bars through the footing of the posts and tie them to the semelles de fondation.

Again, thank you for your time.

Regards,

Lynda

[Ron Avery]

You don't mention anything about getting drawings done for planning permission.  You do know that before you do anything you need to get  a "certificate of urbanisme" for the change of use and a permit de construire for the works?

Your application for planning will have to include drawings showing the means of construction of exterior and interior walls etc.  Might be best to talk to the people at the Mairie, they are normally quite helpful.

[Mr Coeur de Lion]

Hi Ron,

I have done the CU, which was approved, and am in final stages of Permis de Construire.  I didn't include drawings showing the means of construction in with the Permis de Construire, and no one has asked me for anything like that........ yet!   I received an "avis favorable" from DDE a week or so ago for the Demande de Permis de Construire, so I guess I'll have to wait to see what comes back from the Maire.

Lynda

[Ron Avery]

Not sure about where an avis favorable leaves you, maybe its because you have indicated that its not an immediate project.  All I got was a receipt for the application, a rejection/return for more information and drawings and then the Arreté (permission). Usually the Mairie pass on the permis when you get the Arreté, you have to sign receipt for it and its dated as its displayed on the Notice Board.

What you could do is get a couple of devis from builders for the work and see what the builder proposes doing[I]  

[Mr Coeur de Lion]

I did a bit of research and I think the Avis Favorable is the opinion of DDE which is sent to the Maire for him to collate with any other requests for opinions that had to be sent out before giving or rejecting my permis de construire.  I was also sent a copy with a note saying that this opinion is not final but awaiting authorisation delivered by the Marie.   Perhaps it is a new law that DDE sends a copy of their opinion to the applicant as well.  Did you have to go through DDE as well, and did you ever receive a notice of their opinion?

I have thought about getting some builders quotes in, but rejected it on the basis that as a woman, all I seem to get from builders is lots of "man talk" and absolutely no practical information. On reviewing that thought, though, I realised that they would have to put their ideas down on paper for the devis, and that would be of use to me. 

Thanks for your time Ron,

Lynda

[BIG MAC]

If you imagine this as a slice through a typical foundation (Footing) then this will give an idea of what I was Rabbiting on about!

What you are looking at arrives all welded together but back in the day would have been re-bars (Reinforcement bars) wired to links (The black oblong ) the blobs within depict the 'sliced' rebar. I can't say if these are a'typical dimensions but it helps with the principle.

[Mr Coeur de Lion]

That makes a heap of sense to me, thank you very much Big Mac.  I need to find the level that is below the frost line in which to put the semelles de fondation.  I'm hoping that my Maire will know what that frost line is.  It is straight onto limestone, so I don't imagine it would be very deep.  Well, let's say I hope it is not very deep.... :)  I think I will have to do it in sections, as I think that if I dig all the foundations in one go, I will weaken the timber frame of the building. I think I'll be ready for the Olympics after the foundations are finished, without even discussing how I am going to do the assainement!  What do I get myself into? LOL

The beton is dosed at 300kg in your drawing.  Is that a particular "strength" of cement?  Is this something else that I should check with the Maire?

Lynda

[BIG MAC]

Frost shouldnt be so much of an issue with limestone..you can get 'frost heave' in clay soils when the moisture content expands as it freezes I would look to 500mm minimum from ground level to top of the ground beam (The composite structure formed by reinforcement and mass concrete) The mix I can't tell you specifically in the uk I would use C30 phosphate resistant (C30P) Used to be called GEN 3  Ultimately for a small footing you may wish to batch (mix consistently to same proportions) your own concrete.

I would look to cast in one hit even if you need to provide temporary shoring or support, this would create a monolithic foundation and much stronger. If as I suspect you are suggesting you are going to underpin corner posts/piers to the structure then you would need a structural assessment and design I should imagine.  

[Mr Coeur de Lion]

Again, Big Mac, thank you for your time.

I was originally hoping to cast in one hit, but was worried about the posts.  Half of the barn was blocked in about twenty years ago, so I only have about 8 metres across the front and 6 metres on one side where I need to lay foundations in order to block in the rest of the barn.   I had to do some research to find out what was meant by "underpin", which I think means extending and strengthening the existing post foundations.  That sounds like a scary job. :)

I think I need to make friends with a local structural engineer!  Off to the bar..... LOL

Lynda

[Ron Avery]

Linda

I dealt via my Mairie with the local DDE agent  The DDE agent communicated directly by E mail for additional information, after the initial application was made via the Mairie, but the approval was given via the Mairie and signed by the Maire.  There is no consultation period as far as I know with neighbours etc unless what you have been told is that the Mairie (ie commune) has no objection in principle to the plans. 

I think you may have a greater expectation of your Mairie than most of us or have misunderstood what the Mairie can do.  Unless yours is different to ours, they are a secretariat and they don't give out building advice, although certain sections might deal with Fosses etc, and they would expect you to have an architect advise you and draw up your plans, which as far as I can remember is a requirement of works on buildings other than for agricultural purposes.  The DDE also has a duty to see that any works complies with current building regulations.

[Mr Coeur de Lion]

Thanks for your response Ron,

I wasn't aware that I needed an architect for my application.  I thought I wouldn't need them because the size of the barn was less than 170m2.  I also didn't know that I have to include drawings detailing means of constructing the exterior and interior walls. Guess I'll just have to wait for the rejection and start again.  We all learn by our mistakes.

Lynda

[Ron Avery]

Lynda,  you are right that you only need an architect to sign off the plans if the floor area is over 170m2 but you should also be prepared for a demand for drawings or additional information with an application for any building work that produces more than 20m2 of additional floor space, you can do the drawings yourself if you want. They have to see that what you propose meets regulations, but you might get away without drawings if you are not replacing any load bearing walls, the DDE works in mysterious ways.

Have you had formal acceptance of your application yet?  If so, they have 10 weeks to give you permission or refuse it otherwise you can go ahead.

[La Guerriere]

Irrespective of the legal niceties, a lot depends on what your existing barn structure i.e. the posts is standing on. I would not be surprised if the wooden posts do not go very far below the nominal level of the ground: they may just be in holes or maybe standing on odd bits of stone. Excavation for modern type foundations may cause more problems than you think. Also, the barn's load bearing structure goes through the posts, and the infill walls will not be "load bearing". Think this through carefully and maybe dig down beside one of the posts and see what you actually have. You may actually be better off thinking wood infill rendered.

[Mr Coeur de Lion]

[quote user="Ron Avery"]Have you had formal acceptance of your application yet?  If so, they have 10 weeks to give you permission or refuse it otherwise you can go ahead.[/quote]

I do not have formal acceptance of my application yet, but I was feeling quite confident because the recommendation of the DDE to the Mairie has been positive (they have sent me a copy of their recommendation).  I have received a letter that because of the proximity of this little building to a 12th Century Church, that the Mairie reserves the right to take six months for my application.

I only just thought about the matter that you brought up myself.  I will not be replacing any load bearing walls but infilling.  This could be a positive point for my application.  **crosses fingers**

Lynda

[Mr Coeur de Lion]

[quote user="La Guerriere"]You may actually be better off thinking wood infill rendered.[/quote]

Tell me more.... tell me more.  This sounds very interesting.....

Lynda

[La Guerriere]

Maybe some pictures might help all of the contributors ? Can do ?

[Mr Coeur de Lion]

Give me ten minutes and I'll walk over the road and snap some shots

[Mr Coeur de Lion]

From the outside the building looks like it should be pulled down, but the interior timber is in remarkably good condition and I believe save-able. We bought some land next door to us and they included this little barn across the road. One thing that is on my side is that the barn was habited in about twenty years ago (albeit just one room), so the application has been named a "rehabitation" and water, electricity, and assainement are already there at the site.

[IMG]http://i31.photobucket.com/albums/c369/blueblarg/IMG_1643.jpg[/IMG]

[IMG]http://i31.photobucket.com/albums/c369/blueblarg/IMG_1646.jpg[/IMG]

The timber foundations seem to be laid into concrete piers with the timber starting about 300mm off of ground level.  This could perhaps account for why the interior timber is in such good condition because it doesn't touch the ground.

[IMG]http://i31.photobucket.com/albums/c369/blueblarg/IMG_1645.jpg[/IMG]

[IMG]http://i31.photobucket.com/albums/c369/blueblarg/IMG_1644.jpg[/IMG]

Hope this clarifies things,

Lynda

[Pierre ZFP]

Gosh that looks exactly like my old barn.  Wonder if the same chap did it? [:D]

I have to admit I concreted the earth floor, took off the rotting cladding and rebuilt the wall with parpaing then replaced the cladding with pvc cladding so it looked similar to before.  The wall I did doesn't face a road and can only be seen by me so I didn't see a problem with this.

[Mr Coeur de Lion]

[quote user="Pierre ZFP"]

Gosh that looks exactly like my old barn.  Wonder if the same chap did it? [:D]

[/quote]

You can see why I am so eager to do something with it. :) Even if it is so I don't have to look at it when I open my front door.

Lynda

[La Guerriere]

That's great, at least the wooden posts are sitting on concrete foundations to start with, so there won't be any problems of rot etc. The unknown of course is how far those lumps of concrete go. It wouldn't do the excavate past the bottom of those lest the whole thing comes donw like a house of cards ...

[BIG MAC]

A timber infill rendered or even composite panels may be considered however traditional buildings can often be ruined by putting new and inappropriate work against the old. Rendered lath is not a new thing (Think wattle and daub) and some buildings do lend themselves to it (Collumbage type longeres etc)

You need to consider what it is you wish to achieve as a performance specification (Nothing fancy, just state exactly what return you want from the building)

Things to consider......

What is the building going to be used for.

Will it contain kitchens bathrooms.

Will it be used all year round.

Regulatory compliance ...check with the Maire 

Will the benefit of the building once renovated cover the cost (Whether you measure the return in € or enjoyment is up to you)

One decided that you wish to commit to works you will need to define a scheme ie. I want to underpin one side of the building and cast new footings in doorway which is prety much where we started...I want to infill walls in masonry etc...I would tabulate this lot so that you can insert costs of alternative methods of build which may be suitable and insert rough order costs. The costs may well define the scheme you ultimately go for but if you work from what you want from the building out then you should be able to better determine (Value engineer) where best to spend the money and on what.

So once you have that little lot sorted you can then start on the creation of a scope/schedule which details the proposed works and the measurements preferably. From this information you can create drawings (Nothing too fancy) and a detailed list of what you want (You will be surprised when you get the devis of those things that you may have missed)

I would then procure at least 3 devis  and take the lot to the Maire with your scheme to discuss whether the proposals fit with the local plan etc. and what  permits will be required. It is at this point I would ask if  drawings are sufficiently detailed etc. It may be that they insist on an Architect or they may not.

The Maire may insist on some changes which will need to be incorporated but once you have done this then at least you know what is allowed and at roughly what cost.

Job isn't over there though you now need to consider programme and in which order of works will you get the best bang for your buck so you may for instance be able to prop building from virgin ground using Acrow type supports on slabs to allow the underpinning of posts (This would be a simple batching with a cement mixer job) whereas when your ground beam goes in you wont want supports in the way and likely you would use readymix. What else can the readymix be used for if you take a whole load you could prepare other areas to recieve concreete at the same time....etc etc.....

[BIG MAC]

Having seen the pics I would go with.......

1) Small strip footings between posts and dowelled into their footings if they are substantial enough replace them if not

2) A plinth wall in engineering brick or dense block about 3 blocks high incorporating a damp proof course which has floor slab membrane incorporated and aligned to have finished face level with existing timber posts

3) An insulated floor slab (Edges as well as underside) using the wall and insulation as an edge shutter membrane on top of insulating and into same bed joint which carried DPC.

4) Number of choices here but I would go for attaching new green oak horizontal cladding rails with studs as required to support openings and windows, bottom rail will be on top of masonry to will want a DPC beneath it.

5) Plate the building with termite resistant ply or similar then a Tyvek type breather membrane then cover the lot with close boarded or even T and G green oak making sure it passes the masonry by about 100mm

6) You are then free to cut in windows / insulate walls and panel internally at your leisure, trimming out openings again in green oak and making sure key elements like shutters and doors repeat on the little masonry section so that the themes continue.

7) Roof wants stripping and replacing by the looks of it if done in slate and well insulated (Perhaps close boarding then insulating / counter battening prior to slate would look very special

8) New rain water goods (You can get these now in all sorts of colours I think dark grey or copper may well look good once the oak weathers down to its more silver colour..you can accelerate this by painting /spraying with rusty water ie bucket full of old Iron nails chain etc and water)

9) Windows doors internal studwork, services, ventialtion, panelling, trims and decorations.......

again it depends what yo want to use the building as but it could be quite pretty....

good luck.