The best structure for STONE ROOFTILES
Hello people.
I am new here, I have been looking for a discussion group where I could get some advice, but it’s not easy.
It’s about the roof of a cabin I recently bought in Northern Spain, in a protected area. I need to rebuild the roof (it’s about to collapse) and I have (and I want) to keep the rooftiles, that are very heavy flagstones.
For a question of aesthetics and price, I am going to use timber for the rafters, pillars and roof decking. And here comes my question:
The stones are not very regular, so I will need something underneath. What do you think would be the best way to make the roof waterproof?
-Alternative 1: A sheet of thick asphaltic membrane like those used on flat roofs, then the stones fixed on it in some way (stripes of timber, mortar or something like that). I don’t know about how long those membranes last when they are exposed, even when covered by the stones.
-Alternative 2: A waterproof membrane (the thin ones used under the slates) on the roof decking and a layer of cement on it, then the stones fixed to it with mortar. I don’t know if the waterproof properties of the membrane will remain when covered by cement.
-Alternative 3: Any idea will be welcome!
I have a small website where I keep the log of the works I am about to do. Feel free to have a look: www.freewebtown.com/casapollo
Thank you in advance!.
Replies
Holy cow! You have some serious work ahead of you dealing with that stone. I'm no roofer (but I have worked with flagstone quite a bit), and I can't imagine wanting to put that stone back onto the roof. While it may be intriguing to have a stone roof, that stone will be at best a cosmetic treatment on top of the actual proper roof that you build under it (what that may be I will leave to others more experienced to comment on). Why not consider using the existing stone that you have on the roof as a paving material for a patio area or perhaps a walking path. I would think that you should be able to get some very attractive clay tiles that would be very appropriate on your building, and far more likely to actually add to the functional aspect of the roofing system rather than simply being a very difficult to deal with aesthetic curiosity.
Just my thoughts, but it seems you will have plenty of work without the excessive complication/difficulty that trying to reuse the stone for the roofing will bring you.
Kivi
Hi, Kivi.
Thank you for the response. I know you're right but...
Well it's more than aesthetics... The cabin is 200 years old and it has preserved the stones up to now. Also, my idea of restoring the cabin is not the most practical of them all, I am not pretending to be practical or finish it in a forthnight.
Using clay tiles to tile the roof of that cabin in that place would be for me like restoring the Colosseum in Rome with plasterboard, and also at the moment I cannot afford even to think of buying the whole set of tiles. Maybe that's what keeps my innocent idea running, it would be lost if I had lots of money, and I'd just pay some local builder.
That's why I came here and ask you all, otherwise I wouldn't need any help!
Thank you, keep in touch and see if somebody can find me a solution.
m.
cool roof..
View Image
i'd hire one of hte local roofers to show you how to do itMike Smith Rhode Island : Design / Build / Repair / Restore
Mangelhm,
Welcome to Breaktime and know that you'll get laots of advice here.
The is one very nice roof. Are you hoping to restore it exactly as it was, or can you lose some of that stone if it is not needed for watertightness?
How is the stone currently attached to the roof?
SamT
Hello, Sam
Well, not exactly, that would be impossible.
I just want to use the stones as rooftiles, but knowing that I have to build a waterproof roof underneath.
And that's my question for you guys. How to build a waterproof roof to which I can fix the stones in the best watertight way.
m.
Uh, I forgot.
The cabin is almost 200 years old and the stone is NOT attached to the roof, it's just left there, its own weight is the glueing agent. The decking was made with thick logs, straw and raw clay, on which the stones are standing.
Thanks.
so, mangel.... do you think the roof always leaked under come conditions ?
or did they ( do they still ) have a method of laying them so they didn't leak ?
View Image
it looks like the locals knew how to lay them so they didn't leak.. and the longevity of the structure confirms it..
you could build it like they did and cover it with a membrane, then lay your stones..
but i would find out how the locals did it ( do it ).... failing that i would lay them like shkes , with interleaved felt at every headlapMike Smith Rhode Island : Design / Build / Repair / Restore
Thanks for the pic Mike.
Im thinking bulldozer and a new McMansion or maybe some vinyl condos!
I guess I'm just one of those guys that cant see the beauty...
blue
so, the clay is the bonding agent and the waterproofing tooMike Smith Rhode Island : Design / Build / Repair / Restore
Hi Mike.
Thank you for your first approach...
More about the traditional way. The fact is that those cabins were used as shelter for the cattle, that was in the ground floor, with the sheperds sleeping in the first floor where they kept the hay. Let's say that those people were living for the cattle, the cabins didn't even have any window, just ventilation holes!
The roof has been standing due to the sturdiness of the structure (very thick oak pillars and rafters), but asking the locals, I don't think any of those roofs were completely watertight at any time, even windtight.
Hence my idea of creating an insulated and watertight roof underneath. I will probably hire an specialist to set the stones as well as possible, but I want to have something that will last for another 100 years. That's the aim of my quest.
I would like to ask for advice about the materials to use for that watertight layer.
Thank you.
local vernacular usually rules..
and no matter how STRONG the materials were ( oak , etc) they would not have lasted if the roof were not weathertight... kind of like the thatch roofs in england & ireland, if they leak, the roof structure rots..
yours lasted more than 100 years, it didn't leak.. i seriously doubt you can mix modern membranes and those stones and wind up with anything other than a fiasco ( is that a spanish derivation ? )
the clay is the key, and the headlap of the stones is the rest of the solution
if you use a waterproof membrane under the clay, what will the clay "key" into ?
if you eliminate the clay, what will the stones key into.. the whole thing was developed over a thousand years.. or at least several hundred.. the frame, the straw, the clay , the particular type of stone.. they are all local vernacular .. a solution developed by trial & error... the errors didn't survive.... your cabin did.. deviate from the local methods at your risk
but hey, whadda i no ?
anyways... it all looks great and well worth doing.. keep us postedMike Smith Rhode Island : Design / Build / Repair / Restore
Yes, Mike you're right.
The problem comes when we speak about availability of materials, even when they are local materials.
200 years ago the area was covered with oak forests. There are none now, in that valley, the only local produce comes from another valley nearby and I just can't afford it. The same with clay. The soil around the cabin is stoney clay, I guess there are traditional methods to obtain pure clay from it, but...
And the people building these cabins 200 years ago, they are not readily available now. I have seen a local builder using a ondulated metallic layer, then concrete, then the stones. It looks like that's the way now...
And the people building these cabins 200 years ago, they are not readily available now.
You might want to keep looking. Below is a trulli, commonplace today around Alberobello in Puglia (Apulia), It. PAHS Designer/Builder- Bury it!
A product similar to these is what I would use under tile or slate. There's probably something comparable locally.http://www.interwrap.com/Titanium-UDL/titanium-index.htmlhttp://www.rooftopguard.com/Birth, school, work, death.....................
http://grantlogan.net/
Hi seeyou.
Thank you.
But when you use tile or slate you attach the tiles to the roof using stripes of timber and nails or the tile flange. How would you attach the stones to the synthetic layer underneath?
>>>>>>>>>>>>>But when you use tile or slate you attach the tiles to the roof using stripes of timber and nails or the tile flange. How would you attach the stones to the synthetic layer underneath?Slate nails to the sheathing as do some tiles. Some tiles hang on lath. Stone is a new one to me. Slateman may pop in here with some ideas.
I've got a buddy in Spain that does a little roofing. I'm drawing a blank on where he lives now. He might be close to you. I'll see if I can find out.Birth, school, work, death.....................
http://grantlogan.net/
Mangelhm,
The main points, as I see them ATT, are;
Time. One man to do the work as he gets 'round-to-its.'
Cost. Use off-the-shelf-technology.
Waterproofing. It is a roof, after all.
Insulation.
Longevity
Weight.
Strength.
Flexibility. That wooden framed roof will move over time, so rigidity must be minimised. I think the house itself has settled all it's going to after 200 years.
The time constraint means that you must be able to work on one section of the roof and know that that part is able to be exposed to the weather for an indefinate period.
I would layer, from the bottom up, waterproof membrane, (standard roofing paper will be OK,) foam board insulation, galvanized chain link fence reinforcement, Flexible concrete with pozzolans, or light weight flexible concrete, topped with Xypex, then the stone at your convenience.
Plan to work from one gable to the other. Use 4' wide chain link to match the 4' wide foam board. Apply the roofing paper from one eave to the other in a 4'+ wide area, cover with the foam glued down, (apply the glue in verticle runs only so water can flow,) then a single length of chain link from eave to eave. Hang pretensioning weights from the ends of the fencing with something like 100# test monofilament fishing line in a manner that you can clip the line after the cement has set. Be sure the roofing paper runs completely to the eave edge so water can't be trapped under the concrete.
You can then place the minimum 2" thick concrete into the chain link by hand in as large a section as you can comfortably work. After the entire roof is concreted, roll on a layer of Xypex.
Set the chain link and foam 2" back from the eave edges and gable edges to provide weather proofing for the metal and insulation. When placing the concrete, be sure to leave enough chain link exposed at the long edge to tie the next piece into. Roofing paper is cheap, use two layers, but plan it so that you will be able to interweave the next 4' wide section into the previous.
When done you will have a monolythic concrete roof that is setting on the house held in place by gravity with no penetrations thru the waterproof membrane. If you want the extra detail, you could pin it to the stone walls, but the entire wood framing would have to be below the wall height the dimension of the thickness of the foam and you must use rustproof pins at the eaves because they must penetrate the roofing paper.
Tape or spray foam bond the edges of the foam pieces.
The only time constraint will be the foam, which cannot be exposed to UV for very long. You only need to buy enough material at one time to complete a 4' wide section from eave to eave. Chain link can be spliced so there will be no waste to it. Except, of course, the last piece leftover(|:>) The foam, and, if kept dry, the concrete, can be stored until used, so you can buy them as funds become available.
This method should allow you to use the stone as a purely esthetic material. You won't have to overlap them like shingles.
I hope this gives you and your engineer some ideas.
SamT
Hello, Sam.
That's what I call a detailed description. Thank you very much.
Now my comments on it. I'd like to avoid the use of the foam insulation out there, as I have an unlimited supply of free thick poliestyrene panels and I would like to use it for insulation (I though to use it under the decking, between the rafters, and a vapour barrier under it, so the moisture doesn't get trapped between the rafters.
Could those panels be used as the foam insulation you described?If I was to install the insulation under the decking, would it be ok to lay:
OSB panels on the rafters
One or two layers of roofing paper
The metallic chain
The concrete with the waterproof treatment
The stones
Do you think the OSB panels would get degraded with time?
Can the roofing paper keep its properties like this?
Is there any way to avoid the use of concrete?
I hope I am not talking nonsense, thank you again.
m.
I like your thorough approach.
I have a feeling these stones (the larger at least) have some backside chiseling (natural or manmade) to sit in place by gravity.
If one wanted to really mimic the old style, you're going to need more and better selected stone. If I'm not mistaken, schist was commonly used there for roofing stones. Quartzite specifically can be obtained in thin, watertight flagstones. I would imagine these could easily be cut and laid ( by a good local stonemason) as thick irregular slates would be. Even including a back partial slicing to create a holding ledge. And while maintaining a watertight roof.
Seeing that you're in the hills, I'm sure there's some local quarries close by.
You'll need to identify the type, quantity and weight of the finally decided upon stone and be sure your roofing deck can support the load. The type you pick, the quantity your mason will determine, the weight will be figured out by your stoneyard.
I think you'll have something really special when it's done.
Mangelhm,
Sure, that would work. I didn't know, (actually I thought you wouldn't) that you were going to deck it first.
As to not using concrete. Those olde boys who built that roof in the first place set the stones in clay, which can have a lot of holding power if dry, and, like Peter said, I'll bet there is some kind of key that keeps them in place.
The concrete will allow you to cement or grout the stones down. The main purpose of the Chain Link Fence material is to connect the two sides of the roof together so that one side can't slide down without first pulling the other side up. The secondary purpose is to provide a reinforcement to the concrete.
Myself, I would look at pinning each eave stone to the wall underneath, then setting the next higher stone(s) abutting the eave stone, not overlapping, then grouting in between. I know that it is not an exact reproduction, but I feel it would hold better and it would continue the laid stone look of the walls but with much large faces.
If you are going to place the foam underneath the decking, you can apply the concrete only under each stone as you place that stone in position as if you were grouting down a very large tile. You would still have to insure that all the fence material was encapsulated in concrete, but you would only need maybe 1" between the metal and the atmosphere if you use waterproof cement. You can mix the Xypex concrete waterproofing material in with the rest of the mix. It doesn't have to be applied only to the surface.
There are some advantages. You can set nails into the framing so the fencing will hook on them for extra bonding. Just place a blob of roofing tar down and drive the nail thru it. One disadvantage is that you must keep the weight on the two sides balanced as you work your way up to the ridge. IOW, set one eave stone , then set the next one on the other side, then back and forth from side to side.
You can also drill short holes in the back side of each stone and set a hook into that hole and hook the stone to the fencing. Alternatively, if you used an eyehook you could nail the hook to a framing member thru a blob of tar. This would require advance planning and good layout techniques. It is probably the most secure method. If you used rust proof hooks, bronze, cast iron, Galvanized, or stainless steel, and overlapped the stones, you would not need the fencing. Just make sure the hooks and nails/spikes will hold the weight. On the other hand, getting the hooks made will probably cost more than the fencing and concrete.
Thank you again, Sam and all of you, guys.
You make a lot of sense. I like the idea of the fencing grid reinforcing the concrete and at the same time, being hooked to the framing. You put in words something I had as an abstract concept in my mind.
So let's say I use OSB panel on the rafters, then a watertight membrane, then the concrete. Two questions and more, arise:
-Concrete standing directly over the wood would damage it. What kind of watertight membrane would you use? Normal roofing felt? A thicker asphaltic layer? Would they stand the test of time? Would the concrete stick to the membrane anyway?
-Would the concrete eventually crack with ice or change of temperature?
I hope I can save money quickly (I need a job first) so I can start the works. Roofing will be first, then the rest can be done little by little.
m.
Mangelhm,
I am not that familiar with sealing penetrations in any other membrane than roofing felt so I can't address them. I understand that some Ice and Water Shields are self sealing. One of the other BTers may chime in with that info. EPDM is NOT as far as I know.
It is far better that the concrete NOT bond to the membrane so that there is an open channel for water to drain thru. With felt, you can set the nails at an overlap and place tar in between the layers and on top where the nail is going to penetrate. Two layers, each made up of overlapping rows, should last another 200 years barring accidents.
Waterproof flexible concrete should not be effected by freezing. Using galvanized fencing will go a loooooong way towards preventing cracks all by itself. Flexible concrete has fiber mesh added which also helps prevent cracking. In any case, most cracks are the result of either settling of the base, using too much water in the mix, or allowing the mix to freeze before it sets.
If your roof sags again like it did over the last 200 years, the concrete might crack. (|;>)
All that being said, I would be still real tempted to see if Delta-MS or Delta-Drain by Cosella-Dorken would be appropriate for this application. You might want to contact them and see what they have to say about your dilemma.
SamT
Sam , what about a membrane , water proof concrete, a layer of clay , then the roof rocks . I have seen water get under rocks and freeze then it lifts the rock and the bond is forever broken . But the clay will be sort of self healing when the weather turns warm the moist clay will stick itself to the rock . Much like the mud sticks to your boots on a muddy jobsite.
I would use an EDPM and glue it down . No nails , or a I/W sheild that can be nailed .
hey don
Wouln't the clay get washed away and in some years the stones would start moving?
Do you think ice would break the bond, being the stones attached to the concrete with mortar?
The clay is "protected" from the heavy rain It should only be getting seapage.
Any time water gets between hard ojects and freezes it will seperate them . The old stone guys used to drill hole in rock and fill them with water to freeze ,ez way to split the rock.
It sounds good. Just one thing,
how would you prevent the concrete from getting bonded to the felt so there is some space between them so the water drains?
Mangelhm,
I don't know of any way to Make it bond to 'tarred' felt roofing paper. Ain't gonna happen.
But before you get stuck on felt, get hold of Cosella Dorken.
SamT
Your committment to both indigenous building and longlevity is admirable. When I have visited small European villages I have always been amazed at the local ingenuity used to blend modern lifestyles and traditional building. As a last resort maybe you should just buy some cows and not worry about the leaks.
Good luck.
Doug
LOL
Yeah, that would be the last resource, as you say!
I am pretty peculiar with my priorities, I don't care about what most people care about, but I just can't live in a place that is not insulated...
WOw. What a project. Just a note: I saw similar stone roofed buildings in Switzerland. Never got a chance to go inside one but man, did they look cool.
Here's my one thought on accomplishing this project. If retaining the authentic appearance is your goal and you're not entirely purist about how you achieve it, perhaps you might find it easier to build a roof within the roof. In other words, create two framing structures - the inner one could be an ordinary wood-framed roof with any normal waterproof system such as the rubber membrane you mentioned or even asphalt shingles over plywood (or whatever). The stone roof would be a decorative facade. Then construct another frame over the top of it with spaced timbers or whatever system the original builders used to support the stones. Leave a space between and allow water to penetrate the stone roof and fall through to the inner weatherproof roof where it would drain off. I don't know how you'd hide the edge of the inner roof at the eaves and the gables but it seems doable. At least it may be an easier problem to solve than the one of how to create a waterproof roof and attach stones directly to it. If you can build it as I am thinking, the stones would never touch the waterproof membrane. Perhaps the waterproof roof would last a very long time when so protected by the stone roof. On the other hand, I don't know how you'd replace it when the need arose without dissassembling the stone roof. But you'd have that problem either way.