Holding on to your hat, I mean roof

[DrClaude]

TL;DR

How to stop a roof from blowing away in a storm?

@davenn posted the following in the Lame jokes thread:

View attachment 244357

Very funny, but I wonder how realistic this would be. What kind of anchoring could one use that would actually help in stopping the roof from blowing away?

 

[davenn]

Summary: How to stop a roof from blowing away in a storm?

Very funny, but I wonder how realistic this would be. What kind of anchoring could one use that would actually help in stopping the roof from blowing away?

I was considering something like angled stakes into the ground ... very long/large tent pegs

Dave

 

[DrClaude]

I was considering something like angled stakes into the ground ... very long/large tent pegs

Yes, but considering that it appears to be bracing for a storm that could uproot trees, would that any significant resistance to the roof blowing away?

 

[davenn]

Yes, but considering that it appears to be bracing for a storm that could uproot trees, would that any significant resistance to the roof blowing away?

sounds like a job for the mythbusters

 

[Rive]

but considering that it appears to be bracing for a storm that could uproot trees, would that any significant resistance to the roof blowing away?

Trees are standing against the wind and the roots has to deal with torque: a roof (as long as it is still in place) has to deal with the lifting force of the stationary air below. So any type of balancing of the lift works. I have some doubts that those anchors would be enough in a cyclone (especially once the soil is turned to mud by the rain), but the theory behind is right.
Less sophisticated solution is to put stones on the roof.
The traditional way is to make the http://www.traditionalroofing.com/TR7_Norway.html.

Ps.: it http://www.traditionalroofing.com/TR7_Horsham.htmls and beams though... That weight is no joke, the roof alone has enough material to build a modern house...

 

[anorlunda]

It's real! The picture is from the summit of Mount Washington, NH, USA. They claim 100/100 climate there meaning that the wind blows more than 100 mph 100 days per year.

 

[anorlunda]

The Florida building codes revised after hurricane Andrew have been very effective. After Hurricane Irma, I saw a picture of two adjoining neighborhoods. The pre-Andrew standards houses were heavily damaged, the next door houses built to post-Andrew standards were undamaged.

But this is slightly off topic because the OP is about retrofitting existing houses.

 

[russ_watters]

Summary: How to stop a roof from blowing away in a storm?

@davenn posted the following in the Lame jokes thread:

Very funny, but I wonder how realistic this would be. What kind of anchoring could one use that would actually help in stopping the roof from blowing away?

I'm reasonably certain this was discussed before and the answer is yes. The tough part is estimating the lift; you can easily calculate the down-force from the straps using the angles and rated strength.

 

[Steelwolf]

I remember when we did a Navy trip to Australia in the Early-mid 80s and the houses there, like in Darwin, all had to be cable-stayed to the foundation. Cables had to go up inside the wall, contain the roof members and down the opposite wall to the foundation so as to keep them together and not smashing the house next to them also.

So I know that such IS in use in the building field. So while the one Davenn posted was a nice chuckle, I was snrking to myself because that was really done right, with the boards along the edges under the stays to keep the edges from tearing upwards. Truckers are used to the high speed winds and tie-downs, so are not to be neglected or laughed at if they start setting up like that.

 

[jrmichler]

The American Wood Council publishes a Wood Frame Construction Manual for One- and Two-Family Dwellings that tells how to build for winds up to 195 MPH (3 second gust): https://www.awc.org/codes-standards/publications/wfcm-2015.

From their web site: The WFCM includes design and construction provisions for connections, wall systems, floor systems, and roof systems. A range of structural elements are covered, including sawn lumber, structural glued laminated timber, wood structural sheathing, I-joists, and trusses.

A portion of the WFCM is available as a free PDF: https://www.awc.org/pdf/codes-standards/publications/wfcm/AWC-WFCM2015-HWG160C-1703.pdf. The big, bad hurricane will not blow that house down. The interesting part is the importance of many details. Just pulling a few cables over an existing house is not necessarily very useful.

 

[Averagesupernova]

Usually the key to keeping a building from coming apart in a storm is to not let anything get started. The overhang on the gable end of the roof is often a place that comes off first.

 

[Dr Transport]

 

[Baluncore]

Dynamic pressure that enters the building through a broken window or open door on the windward side can lift sheet roofing by pulling the fasteners through the sheet. Wind flowing over the house and roof structure can generate lift.

Dynamic pressure against a steeply sloped roof can apply down pressure. The walls are designed to support the weight of the roof. If you add load straps to hold the roof structure in place, you might crush the house or eves, but you must expect to lose some sheet roofing from between the straps.

Once a few sheets are gone, or have opened like flaps, the differential pressure will be relieved. So why not build slats into the roof that will lift automatically to relieve internal positive pressure? Is it because the ceiling will then lift? But the ceiling is usually attached to the bottom of the ceiling support, so it should remain in place as the fasteners will not pull through.

 

[Rive]

So why not build slats into the roof that will lift automatically to relieve internal positive pressure?

When all this is relevant rain 'falls' ~ horizontally => roof with any type of holes is just like no roof.
I think when it is about building it wind-proof then there are just more simple solutions than slats, like 'nailing it down' in various ways or making it heavy or so.

 

[Nik_2213]

IIRC, the traditional crofter or 'fisherman's cottage', usually situated on a storm-blasted exposure, would use old nets and hefty 'guy ropes' anchored to large rocks / boulders to hold the roof down.

Nearest I've been to such conditions was camping on Anglesey, Wales (UK). The weather forecast promised a 'real roarer'. These days, it would be an infamous named storm. Then, the 'shipping forecast' just listed near-apocalyptic sea-states in most areas, worse along the core's track.

We had a big Marechal family-tent, with the optional steel frame rather than the default alloy. Still, we double-pegged the feet, double-guyed and triple-pegged the guys, turned back turves for a diversion drain. We filled our two GRP kayacks with enough water to anchor them. And, yes, tied them down, to be sure, to be sure. We collapsed the tent's kitchen annex, the door and window screens, tied them down. Then we cross-guyed the tent to the close-parked car's bumpers (fenders) and long roof-rack. We also parked our well-anchored baggage trailer as a secondary wind-break, for the direction would so swing as the storm's core passed.

We didn't get much sleep. At times, the wind noise was literally deafening. Despite our precautions, a torrent over-flowed our drain, but ran safely beneath the rippling ground-sheet. Happily, the storm blew through by breakfast. As usual, I headed out with our 3-gallon water container, en-route to the site taps. This day, I just stopped and stared.

The site had been FULL, late-comers wedged into gaps.

Now, there was but a forlorn quilt of pegged groundsheets, plus two tents. Us, and a tiny 'bivvy' tent. We were safely in-situ. The bivvy tent and its occupants were stuck in the big hedge at the down-wind end of the field. For that young couple, the Earth had truly moved...

 

[some bloke]

I imagine that the wind will snag the overhanging eaves of a rook, and that you can make it more storm-proof by making the join as aerodynamic as possible. If you can put shutters to keep the wind from getting into the house, you can just focus on the external aspects. Once the wind is in your house, I gather the best option is to open all the windows and stop the house getting pressurised.