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Rafter ties

One very important structural problem that I look for on every building, but especially on detached garages, is the top of the wall pushing out.  Here’s a short but (I hope) thorough description of the problem, the cause, and the solution.

Most roofs are built so that the roof rafters lean against the ridge board, or even just lean against another rafter without a ridge board.  Then the rafters are nailed in place.  The other end of the rafter sits on the top plate of the outside wall.  Older roofs were almost always built this way.

So let’s look at this in the direction straight along the ridge beam.

Gravity is pushing down on the ridge board and the rafters, and maybe that’s even helped along by a big snow load.  There’s nothing holding the ridge board up – it’s just there for the rafter to lean against.  So the whole thing tends to settle a little bit.  And when it does the bottoms of the rafters naturally want to push out, and this takes the top of the wall with it.  This happens fairly easily, and the leverage from the bottoms of the rafters will easily pull out any nails that are attaching the top of the rafter to the ridge board.

This problem is especially bad with hipped roofs, because there’s really nothing holding the ridge board up.  On gable roofs the problem isn’t usually quite so bad, because the gable wall provides some support to hold the ridge board up and prevent it from settling.

To fix the problem, or to stop it from happening in the first place, a rafter tie should be installed.  This is a horizontal piece that attaches to the bottoms of the rafters.  It creates a very stable triangle shape and holds the bottoms of the rafters and the tops of the walls from pushing out.  A rafter tie is typically a piece of 2x lumber, but it could even be a metal cable or chain as long as it’s securely fastened.  And you don’t need a rafter tie at each pair of rafters.  In a detached garage you only need a total of two or three rafter ties to make the structure nice and stable.

In houses with cathedral ceilings, where you want the open vaulted ceiling and you can’t tolerate a rafter tie, the ridge board needs to be very solidly supported at both ends all the way down to the foundation.  Then it becomes a ridge beam instead of a ridge board.  Since the ridge beam can’t settle, the rafters are held in place and won’t push out at the top of the wall.

R-22 Air Conditioner Refrigerant

Most air conditioners that I see these days use R-410A refrigerant, but some older AC’s still use the old R-22 refrigerant (normally called Freon, but that’s just one brand name).  And R-22 is a problem.  It’s a hydrochlorofluorocarbon (HCFC) and it contains chlorine.

Several decades ago we realized that chlorine gas was causing damage to earth’s ozone layer.  And R-22, by far the most common refrigerant used in residential air conditioning systems, contains chlorine.  So back in 1987 the international community came up with the Montreal Protocol and agreed to phase out the production and consumption of ozone-depleting substances.  In fact the Montreal Protocol was the first United Nations treaty that achieved universal ratification; every country voted in favor.  R-22 had to go.

Eventually air conditioner manufacturers came up with R-410A refrigerant, a hydrofluorocarbon compound (HFC), and the transition began.  R-410A is often called Puron, but again that’s just one brand name for the same chemical compound.

Beginning in 2010 the production and importation of R-22 was limited, and starting on January 1, 2020 it will be prohibited.  Because of these limitations the cost of R-22 has already gone up tremendously, and it’s only going to go higher.  The only source of R-22 will be refrigerant that’s removed from old air conditioners that are being discarded.

Because of their differences R-22 and R-410A aren’t interchangeable.  You can’t just add R-410A to an old air conditioner.  In fact there’s really no substitute at all for the refrigerant in an old R-22 system.  So if you have an air conditioner that uses R-22, and you have a leak or a problem and need more refrigerant, you might be in for a big shock.  The refrigerant might be crazy expensive, or you might just not be able to find any at all.  Then you’re stuck.

In this case your only real option is to replace your air conditioner.  This would entail replacing the outside condenser, the inside evaporator coil (that’s generally in the plenum just above the furnace), and you’ll even need to replace the refrigerant lines that run between the condenser and the coil.

That’s a lot of work and a lot of expense.  But that’s what it takes to save our ozone layer.

So how can you tell what refrigerant you have?  Look on your air conditioner’s data tag outside.  It should say somewhere what refrigerant it uses.  If it says 410A like in the picture above then you’re in good shape.  Otherwise you might be due for a total replacement the next time you have an AC problem.