I am about to build a new house for me which will be an ICF house.  I live on an island off the north coast of Scotland where there is little experience of ICF and so I am going to be doing the job myself.

The house design has gable ends and the roof will probably be formed with attic trusses (much cheaper than SIPS).  The winter brings lots of gales and so keeping the roof on is a priority!

I am fairly comfortable with the idea of bolting the wall plate to the top of the ICF wall and attaching the trusses to it.  What the manuals don't seem to tell you, however, is how to attach the roof at the gable end.  Is there a standard way to do this?  For example, should I:

1. Attach a wall plate to the top of the gable and attach the roof to that?

2. Attach some timber through the foam into the concrete on the outside of the gable and attach the roof to that?

3. Attach the roof directly to the concrete of the gable?

The roof construction will probably be boards on top of the rafters and then slates nailed to battens on top of the boards.  Because of the strong winds I want to keep the overhang over the gable fairly small.

Thanks very much for your help.

Andrew

Andrew,
The typical 12" j-bolt every 2 or 3 feet - perpendicular to the concrete gable would probably work fine. However, if your winds are really strong i would look into something like Simpson Strong Ties -- they come in all shape and sizes and you can basically anchor them to the concrete (preferably wetset) and your roof will would have to splinter into pieces before it can come off. Regards.

Sounds like you're going to have high winds. Might want to attach hurricane ties  with all of the rafters. Cheap insurance.

I would recommend holding down your ICF end gables to allow "look-out" framing of 2x4's or 2x6's on edge to run perpendicular into your trusses and extend over your ICF gables to provide an over hang. This is the most structurally sound detail there is at this location. So, the 2x is "tied" into the truss and connected at the top plate and cantilevered to provide your over hang at the end gable.

Of course you would want to use "hurricane clips"! Depending on your wind loading in your area will depend on the type of clip you use. Check out Simpson hardware to determine the up-lift capabilities of each type of clip. An engineer would typically size the clip.

Good luck on the project!

Thanks very much for the suggestions. I am afraid that I need to ask a few questions to make sure that I understand them!

By "holding down" the gable do you mean make it slightly lower than the top of the trusses?

By "top plate" do you mean a piece of timber laid into / onto the top of the gable and held down with J-bolts (i.e. same sort of thing as with the walls at the side?)

In the UK, the common way to do a gable end is to build what we call a gable ladder that runs along the gable with the "rungs" supported on the brick or blockwork. One side of the ladder is nailed to the last truss (i.e. within the roofspace) and the other side of the ladder forms the outer edge of the overhang. One idea that I had was to build a gable ladder and attach the "rungs" with J-bolts to the gable. The rungs would be inset into cutouts in the foam prior to the pour so that the gable was still flush with trusses. As I don't want much of an overhang, the outside side of the ladder would be directly against the foam and, as far as I can see, ought to be totally secure.

Here is an example of what I am referring to as "look out" framing. This is all wood frame but I think you will get the idea.

http://www.awc.org/pdf/wcd1-300.pdf (page 43)

How restrictive, or prescriptive, is the building code you need to comply with? That very well may control what you can and cannot do.

It sounds like you want essentially no overhang at all on the gable end, like maybe 2" or 3" (5 to 8 cm), correct? How about constructing the ICF gable to a height just below the truss plane, the thickness of a timber? What is your standard timber thickness? Here it is 1 1/2", ~4 cm. Put a timber on the flat on the gable the same as the top wall plate on the side walls. Then fasten one or two thicknesses of timber on the flat against the gable foam with J bolts, or other anchor bolts passing through the foam into the concrete, to form the eave box frame. Nail your roof sheathing directly onto the plate and the eave timbers. This way you won't have any hollow space, nor a significant overhang, in the eave to catch wind. You avoid the time, cost, and hassle, of building the ladder. By the way, what you are describing as the ladder sounds exactly the same as the p43 illustration in the PDF attached above. The only reason for the ladder is to provide a strong cantilever construction past the gable wall. With a very short overhang cantilever strength isn't needed. The only thing you would need to be careful about, I think, is to make your eave so that it will be able to breathe, i.e., not trap moisture laden air behind the trim around the timbers. The typical box eave readily allows for venting.

If the building officials approve I think this will give you what you want, a no wind catching overhang. You probably won't find anyone in the States who would be willing to do this simply because of the appearance of no overhang, but it makes sense to me.

Is Simpson building hardware available in the UK? If not, surely you have a similar product line available. They offer several types of steel strap connectors that are nailed to both the top wall plate, or the wall, and the trusses, or rafters. Their intent is to physically hold the roof down to the walls in the face of strong winds pushing up on the overhangs. You can use them on both the wall sides and gable ends. The website is www.simpsonstrongtie.com.

I just found the answer - http://www.strongtie.co.uk/

Thanks very much for your suggestions. You have summed up very accurately what I am trying to do. My neighbour had quite a big overhang on his roof and he lost part of the roof a few years ago in a big storm so we are trying to avoid that! I sense a discussion with building control coming on!

I spent quite a while yesterday going through the Simpson StrongTie UK catalogue and they have some high wind straps that would probably be very suitable.

The picture in the link above is very similar to what is done in the UK. The only difference is that over here the ladder is built with two sides and one of the long sides is nailed to the final truss, rather than the individual "rungs" being fixed to the truss.

Thanks again for your help.
AA

AA,
I am late to this party, so to speak. If you have not made a decision yet, consider this.
If the overhang will only be a couple inches:
Make the ICF gable wall the same height as the top of your roof trusses/rafters.
Hold the concrete down the thickness of a standard timber (1.5"?)
Set j bolts (or eq.) in the concrete with no more than one timber thickness of exposure.
Attach a treated timber with the nut and washer of the j bolts countersunk level with the top of the wood.
Attach a treated timber to the outside of the ICF with screws through the outer ICF panel and into the wood plate and/or concrete.
Attach any additional wood (if needed) to achieve the desired overhang.
Attach your roof sheathing (plywood?) to trusses and extending over the ICF wall and overhang, holding it flush with the outside of the overhang.
Make sure you over nail/screw the sheathing to the top plate of the ICF wall.
I, personally, would hold the overhang to no more than the thickness of one timber (1.5"?). This configuration would be extremely difficult for strong winds to lift off the house.
If this is of interest, and you want more information, PM me and I will send you a section drawing.

Thanks Wes. I have sent you a pm.

Consider using a 5/8" galvanized carriage bolt through the overhang rafter, ICF, and last (inside) rafter every two feet. Countersink on the face of the pressure treated overhang rafter. With the ICF slightly lower than the top of the rafters the carriage bolts will be well embedded in the concrete. See attached pictures.

@ Skipper Smotherman - Thanks for your suggestions. Maybe I'm not doing things right but I can't see any pictures.
AA

Sorry. Try links now.

Thanks very much. That looks a possibility.

Andrew,
I built Storm Proof ICF houses in South Florida. I have 5 houses that have been through two hurricanes. Wi9th no damage.
The best ICF is Fox Block.
The worst thing you can do to a house is put a gable in the roof. The overhang of the roof is a handle for the wind to grab and it will lift the first 4 ft of the roof off and the wind and the rain will hit the interior ceiling and knock it to the floor. Thousands of examples of this wire in Miami when hurricane Andrew came through.
Also a gable acts as a hinge at the top of the wall. If you absolutly have to have a gable, then use J bolts to bolt the plate down, X brace the gable wall back into the interior 1 1/2 times times the height , every 3 ft along the length. Use ring shank nails to hold down the sheathing. Every 6" along the edge of plywood and 12" c-c in the interior. Put a water barrier over the sheathing and below the shingles. Better yet use metal for the roof. Spray the underside of the trusses with closed cell foam. This will hold down the roof in any storm and insulate the attic.
Close the soffits with foam, do not vent the attic. do not insulate over the ceiling. Put your HVAC (if you have one) anyplace but the attic. Make sure the duct work is really sealed.
You will have a storm proof house that is the most effecient, cheapest, quitest house you can think of.
Regards
Joe
[email protected]

That sounds scary, Joe. Just so it's clear, the gable in my case is going to be ICF so I shouldn't have the hinge issue (I hope!) but I take your points about the overhang acting as a handle. That's why I want to keep the overhang small.

Andrew,
You are correct. With the ICFs forming the gable, the hinge effect that Joe was discussing will not be a factor for you. Different architectural styles produce much very large differences in how a structure reacts to various environmental factors. So it is very difficult to equate what Joe does in FL to what you are doing in Scotland because of the very different architecture. In your case the overhang will be the determining factor. A near zero gable overhang and a small eave overhang will reduce the possibility of wind induced roof removal. Look at how the older homes in your area were designed. They didn't get to be 'older' by being inappropriately designed for their environment.

Thanks, Wes. Interestingly, the design of our house includes gables because they are a traditional feature of old crofters' houses. Scotland uses a lot more of the "room in the roof" type designs than England so while hipped roofs are common in England, they are a bit more of a rarity up in Scotland. Shetland, where we are, has some extra challenges because of the wild winter weather. It doesn't get that cold, just very windy. As a result, ICF is a logical choice for up here but it has been slow to take off. (Ours will be only the third ICF house in Shetland). Masonry, i.e. blockwork, construction is not allowed up here because of the wind.As you might suspect, big eaves or gable overhangs just don't happen up here!

Hi Andrew. Since you are building in N. Scotland I suggest you speak with the folks here: http://www.op-deck.nl/ An insulated concrete roof may be just the ticket for you! FM