Storm-proofing a high-performance home – Ideas?
CZ6, Ottawa Ontario
On Friday the 21st, Ottawa/Gatineau (Canada’s National Capital Region) was hit by three tornadoes that did considerable damage (EF3) to the affected areas and caused widespread power outages. Killer tornadoes are not common around here, but as the builder of a new home I’m wondering how I can effectively “toughen” the structure without compromising its energy efficiency.
A few questions:
1. Bonded Sheathing. Can OSB or plywood sheething be bonded to exterior wall studs to increase racking strength? I ask because AFAIK there is supposed to be a 1/8″ gap left at panel edges for expansion/contraction. Would construction adhesive between the sheething and studs be an issue?
2. Hurricane Ties (for roof truss to top plate). Traditional ties can be difficult to air seal. Timberlok truss screws seem like a much better solution from an air sealing perspective. I don’t believe either are required in my area but I’d like to give the roof some extra security. Are there other options I should know of?
3. Tension Cables. These are cables anchored into the foundation through the sill plate and extend up through the walls all the way to the top plate of the upper most floor. Tension in the cables keeps the top plate secured firmly to the wall. Good idea? Bad idea? Is there a better or more practical solution that’s less invasive to the wall?
4. Window Security Film. Security films can increase a window’s penetration resistance by a pretty large margin, which could help in defending against airborne debris. Our climate zone dictates high performance windows with high performance coatings. Could the application of an interior or exterior side security film affect the performance of the glass package?
5. Backup Generator. Do you think the added cost of an inverter generator is worth it mainly for backup use? I was looking at something like the Honda EU7000i ES. I’ll need a decent generator on site while building and I’d like to buy once, so something that can run a powerful dense-packing cellulose blower as well as serve as home backup would be nice. A nice-to-have would be the option to run on propane or natural gas, but I have not come across such a unit.
Any other tips or tricks to making a more storm resistant structure? I’m not going to build with ICF, the cost is way too high.
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The destruction zone of a tornado is usually fairly narrow- a couple hundred meters would be a wider than average. The kilometer-plus with tornados are pretty rare (but do happen) in the southern portion of the US "tornado alley" plains regions. Most are narrow, but right in the track the damage is quite severe.
Short of building the walls & roof with reinforced concrete there isn't much that's going to save the major structure of a house in a direct hit. A quarter kilometer away from the center of the track there may be (repairable) damage, but it's not going to knock the house off the foundation, lift the roof off, or break the walls.
Increasing the racking rigidity may increase the likelihood of walking the walls off the foundation when closer to the devastation track- some amount of flex can be a good thing.
Unvented roofs reduce the amount of uplift force experienced by the roof deck, at least until the first window is breached. Tightening the fastener spacing on the roof deck helps retain the structural roof too.
Window film isn't going to do much in the face of demolition debris being hurled at highway speeds (or higher), which can happen even a few hundred meters from dead-center along the path. Unlike hurricanes the advance warning period isn't long enough to allow installing sheet OSB/plywood over the windows. Automatic steel storm shutters of the type often used in new construction in hurricane-prone Florida could work, but is that really rational in Ottawa?
Backup generators make sense in areas that experience power grid failures on a frequent basis. What makes sense in a hurricane prone zone doesn't always make sense in less stormy Ottawa with first-world grid reliability.
All the things you are considering cost money and are hidden in the wall. Most buyers will not care about what is hidden in the walls and will not see it as adding any value to the home.
Let’s be honest should house that direct hit from a tornado nothing will save the house. The best you can do is build a safe room that could protect the people. In the end insurance will pay for the damage as long is the house is built to code. There is no discount for building beyond code.
With that said I did screw down all my trusses.
I think getting a temporary power box on site is less expensive than the fuel the generator will burn. It is a hassle to haul fuel and generator around if you leave it on site you risk it being stolen.
Walt
FEMA has a document that may give you some ideas: https://www.fema.gov/media-library-data/20130726-1708-25045-9326/chapter7.pdf
It’s more geared towards new construction though. The easiest retrofit I can think of is to run some threaded rod from the foundation, up through the wall, and bolt it to the top of the top plate. Strap/screw each truss to the top plate. Use grade 5 threaded rod, the regular hardware store stuff isn’t actually all that strong. If I personally was designing something like this, I’d use grade 5 threaded rod, a heavy flat fender washer on top of the top plate, a grade 5 nut, and then a grade 2 or other soft steel jam nut after that. The jam nut of slightly softener material will deform a bit against the other nut and will stay tight. You’d want something that wouldn't loosen with vibration, and you can’t use lock washers against the wood since the wood will flex so it won’t stay tight. I’m not sure I’d trust a nylock for this either. The type of foundation connection would depend on what type of foundation you have. You need something that is strong in tension. For a retrofit, I’d think epoxy anchors.
Regarding a generator, you have 3 main concerns:
1: how much power do you really need? Do you want to run everything, or can you get by with just a few critical loads? A large generator that runs at a low average load but is sized to run a large load occasionally (like an air conditioner) will be less fuel efficient than a smaller generator running at a high average load percentage.
2: how long do you expect your power outages to last? 1800 RPM generators will last MUCH longer than the more common 3600 RPM portable generators you see at the box stores. 1800 RPM generators also cost more. The difference in engine life is usually hundreds of hours for the 3600 RPM units and thousands of hours for the 1800 RPM units. This becomes important if you have frequent or prolonged outages.
3: what fuel sources are readily available in your area? Gasoline is available everywhere, but it can’t be stored for very long (it begins to degrade in less than a year), and can you get it when you need it in an emergency? Diesel fuel is a much better option if you want a liquid-fueled generator, but they tend to cost more. Do you have a reliable natural gas supply? If you do, use it! Natural gas is the best option for residential backup power where it’s available. Natural gas generators can also be setup to run on propane in most cases. Natural gas is almost certain to be the cheapest fuel option as well.
If you want a portable unit that can run on natural gas, look for the “dual” or “tri” fuel units. They are out there, and they’re not terribly expensive. Personally, I would want a permanently installed unit, either natural gas or diesel if natural gas wasn’t available, and an automatic transfer switch for the entire house. The portable units have a habit of not working when needed in an emergency although I suspect that’s usually due to a lack of maintenance.
If you do decide to use a portable unit, make sure to either use a transfer switch with an “inlet” (like a plug, not a receptacle, that mounts on an exterior wall to make connection of the generator easy), or make sure you have enough extension cords on hand to run all your critical loads. Please don’t be tempted to use a “suicide cord” (male plug on both ends) and backfeed your house — doing so is very dangerous.
Bill
Hi Dana,
Agreed, the chances of suffering a direct hit are pretty low, especially in an area that's not prone to tornadoes to begin with. My train of thought was more along the lines of, if I'm building from scratch already, why not incorporate some survive-ability details if they don't cost a fortune? The hurricane ties and bonded sheething certainly fit that description and could potentially increase the resilience of the structure.
Absolutely, there's no need to build a coastal Florida style survival bunker house where we are. I have large overhangs planned (36"-96") so keeping the roof attached is a valid concern, even in non tornado force winds. I will need hurricane clips in at least one area just to keep my Engineer happy at design wind loads.
Good point about fastener spacing on roof sheething. This is another area where bonded sheething might make sense. Any thoughts on whether bonded sheething is acceptable on roof or exterior walls?
Window film certainly won't stop a 2x6 shot out of a cannon, but it takes far less than that to breach an unprotected glass window which then allows the whole house to pressurize. We're building on a 3 acre lot so houses are spaced well apart. I would think the majority of debris I'd be concerned with would be trees/branches and other things picked up off the ground, and I could see a good window film helping the window stay intact than it might otherwise.
If you haven't before, check out the videos posted by 3M demonstrating the effectiveness of their security window films.
Hi Walt,
We're building this house with the intention of staying there for the next forty+ years. Resale value would not be my motivation for making the structure more robust. Like you, I do see value in screwing down my trusses, which is what led me down this path of looking at the rest of the structure.
Good points regarding the generator on site. I do plan to ask about the temporary power box, I had just assumed it would be expensive.
Hi Bill,
Your suggested threaded rod assembly is pretty much the same idea as the Tension Cables I mentioned in the original post. I see value in this approach, especially given the generous roof overhangs in our design. I'm not sure how closely they need to be spaced, but I guess I can work backwards from the roof lift numbers to get an idea.
A decent approach is suggested in that manual you linked to, in that vertical strapping can be used between the studs, plates and rim boards or even into the foundation. This approach wouldn't really give the pre-tensioned structure that threaded rod or cables would, but it might be the 90% solution and would be pretty easy to implement and for a pretty low cost.
Great input on generators as well, thank you. I'll take some notes for sure.
Lance,
Using adhesive on the sheathing doesn't do anything reducing the spacing of fasteners wouldn't do. Nail off everything at 3" oc. and make sure not to over-shoot the fasteners.
There are Simpson structural connections to form a continuous path from foundation to roof. They are commonly used in seismic design. The advantage they give is that because they connect wood to wood, they aren't susceptible to seasonal movement and shrinkage the way tension cables would be.
Hi Malcolm,
I'm still leaning towards using construction adhesive on the sheething. When you think about floor sheething, screw-and-glue is the recommended approach for a floor with long-term durability. Squeaks are usually a sign of loose fasteners and/or an area where the glue didn't take. The way I see it, a wall is basically a light-duty floor construction: joists and sheething vs studs and sheething. Framing walls on 24" centers means fewer connection points as well.
Good points about the tension cables. Yes, I think I'll have a good long look through the Simpson catalog and see what they offer. Probably a much easier implementation as well.
Lance,
Adhesive probably can't do any harm. We don't use it out here in high-seismic areas because the initial shock of an event needs a small amount of give in the structure to avoid damage. That problem isn't really there in the storms you are anticipating.
Here is how we typically tie things together from foundation to roof:
- As well as closely spaced anchor-bolts, we epoxy 3/4" threaded rods 12" into the foundation (In our case at each end of the shear-walls). The top of those gets connected to a double stud with this:
https://www.homedepot.com/p/Simpson-Strong-Tie-12-3-8-in-Tension-Tie-HTT4/204842329
- Another one is used upside down to tie the studs to the double top plate.
- The trusses are connected to the top plates with clips or truss-screws.
- Sheathing ties everything together with boxes and boxes of nails.
I have the Honda generator you mention. I had an electrician wire a receptacle on an outside wall. It goes through the wall and is wired to the panel, such that it only energizes any circuits if the main breaker is off.
The generator is very quiet and has electric start. I run it for fifteen minutes or so every few weeks, to keep the battery charged. It'll run pretty much everything ( include minisplits) except the oven, although clearly not all at once.
I keep three five gallon cans of gasoline in an outdoor shed. I date the containers when filled and once the gas is more than a few months old, I dump it into a vehicle and refill it, so I always have fresh gas.
Thanks for your thoughts, Stephen. Your routine sounds similar to what I have in mind. There's not much in the way of reviews for that generator so it's good to hear from someone with first hand experience.
Adhesives don't fail in a ductile manner. They break all at once. The nails bend back and forth to dissipate energy and allow the structure to fail in a predictable way.
Very true, Tim. The added strength of the adhesive would hopefully keep the wall from failing altogether.
The nails will still be present should the adhesive fail, however if a bonded wall assembly such as this was to fail in shear, the loads involved would probably make the nails irrelevant.
I have thought about this if i ever build a house and agree some extra features for modest cost would be worth it.
That said you can only do so much but i think solar plus battery would be better then a generator.
That may sound ludicrous but allow me to explain.
When you use a generator you are limited in blackout energy duration to how much fuel you have on hand. Plus the equipment is complex and if your not on top of maintenance or its aged it will not be very reliable.
With a solar system your generating power and storing it so in theory sized properly you would never run out of power even if the grid never came back. On top of this you can use your solar and battery to reduce your energy bills the 99.9% of your life when grid power is running, saving you money everyday.
If i were you i would integrate solar and a battery (the Tesla powerwall allows you to optimize your usage and storage to arbitrage against time of use charges using most if not all your energy on off peak prices and to maximize your own solar consumption or revenue from selling to the grid). Then i would make sure the house is well insulated above code for energy savings and heat retention in case of winter power or natural gas cuts. This can be calculated and insulation level planned for payback or resilience. Finally make sure your insurance is comprehensive.
Alan, solar is definitely in the plans, though it won't be added until some time after we move in. Perhaps years after we move in. We'll see how things go with utility prices, solar prices etc.
The house is designed FAR above code requirements. Not Passive House, but probably in the higher end of "Pretty Good House" territory.
A Tesla Powerwall is a very costly proposition. Just one Powerwall eclipses the cost of a nice whole-house sized generator by a factor of 3-4x. The way I see it, investment into energy storage doesn't have a reasonable payback period yet and likely won't for some time.
Also, I'm in CZ6A in Ottawa, Ontario. A power outage in January with anything other than gas or propane heat would not be feasible with only battery backup - there's just no guarantee of decent sunlight and heating demands are large, even in an excellent envelope. Being off-grid with heat pumps would be my ultimate goal, generating, storing and consuming my own electricity, but a gas generator is still required in that scenario as you could never store enough energy to get through more than one winter day without sun.
Let's see where we're at in 10 years. Maybe costs will shift, new battery technologies will come to market, PV efficiency will jump and heat pump efficiencies will continue to evolve enough to make it all sensible.
I would design for solar now, the wire chases, the weight, the mounting points.
The cheap generators you buy from a big box store are much cheaper then a Powerwall (they are also far less durable) but compared to something like a Generac whole house backup its actually quite competitive. And as i said it gives savings the entire time you own it, you can use it to escape peak power costs and you can bank your own solar which you won't be doing with a gasoline generator. However the powerwall and solar will continue dropping in price in the future as you mention.
I would run some numbers because it feels intuitive that you can't get by with solar/battery but its certainly doable depending on the house design, especially with a good net zero home and a heat pump it would not be as impossible as you might think.
That said i can't blame you for having propane or other backup, but as i mentioned that would only last for as long as you have fuel for.
Solar is definitely in the plans. The next version of our Ontario Building Code will apparently include a requirement for new construction to be pre-wired for solar. I intend to meet that future code requirement when I build, regardless of whether it's enforced at the time of the build.
I definitely don't deny the benefits of solar with battery backup, but I do question the cost. Using the Powerwall as an example, the GenII product offers WAY better value than the original, and they were announced within 18 months of each other. I can only assume a GenIII version will continue that trend and be announced within a few years, further improving the value.
Perhaps the GenIV will be the product that entices me into the technology. A grid-tied net-metering PV array will happen long before I get into battery storage, that's for sure.
I looked into battery backup instead of a generator. The cost was absurd- $14k for a Powerwall that stores $2 worth of electricity. The other problem is that, at least for the two systems i got quotes for, you'd still need a generator for extended cloudy periods during outages. And you couldn't charge the battery with a generator. Someday battery storage may be cheap enough, but not yet. It may make sense if the utility rate structure includes time of use rates and gives a premium for exports to the grid during times of peak demand. ( On Labor Day ISO NE reported peak power prices hit $2.67 per kwh.)