The link between Hot Roofs and Parrots.
By Glenn Hooper Feb 23, 2015
An excerpt from Wikipedia (http://en.wikipedia.org/wiki/Parrot)
“Parrots, along with ravens, crows, jays and magpies, are among the most intelligent birds, and the ability of some species to imitate human voices enhances their popularity as pets”
All the rage these days is to make the attic a conditioned space, by insulating the rafters, and bringing the attic space into the envelope, adding to the conditioned space IS NOT always what its cracked up to be ! I look around the web and see so many experts suggesting this, and doing so without even knowing the project. It is a shame that most can only repeat what they hear.
I think its more of a shame that some people are being misled. They spend large amounts of money by spray foaming the rafters and gable end walls and expect a huge savings. In the case of new construction often times its the only option given to the owner and has nothing to compare other methods to, so just assume they have come out ahead of the game.
Am I saying that its never advantageous ? Absolutely not. What I’m saying is that there is a larger chance that your bills might actually be higher than the other so called experts would want you to believe. Not everyone will benefit from this practice, and each situation should be evaluated on all the factors involved.
What are some of the factors involved you ask? Before you decide to convert a normally insulated attic to a “Hot Roof” you must consider at the very least the following items;
- Current duct leakage to the attic.
- Current ability to seal ducts.
- Current duct insulation values.
- Current attic insulation levels.
- Current attic insulation type.
- Current rafter depth.
- Current air leakage from home to attic.
Talking about how the items above interact with this new fad will hopefully create people who can think on their own and not become a parrot who just repeats what they have heard.
Not all ducts have the majority of leakage in the attic !. I have personally seen a house that leaked more from everywhere else but the attic. While this is not typical, there are many variations. Point is, everyone wants to tout about duct loss savings without even knowing where the losses are coming from.
Ability to seal the ducts, I have seen many homes where there was zero duct insulation and all of it was accessible from the attic. Sealing ducts is terribly inexpensive !
Ducts with no insulation. Its much much cheaper to insulate the ducts, plain and simple. In addition, why would any one want un-insulated ducts to heat an area that’s not habitable ?
Current insulation type and level. Talking about this alone is opening up a can of worms. More than likely your attic has fiberglass insulation. Im supposed to say fiberglass is a great insulator. A parrot might say it depends on how well the fiberglass insulation was installed. What you must know is that insulation is like the hull of a ship. It doesn’t matter if the hull is 10 feet thick or 1 inch thick, if there is hole, the ship will sink. Fiberglass is difficult to install perfectly. Whats more, if you read this far, is this little perl of information for you, The R-value of fiberglass is figured out at near room temperature. The effective R value drops as temperatures drop. Long story short is that the colder it gets, the lower the R value is. What can be done ? Is all hope lost ? Never. Blow good old fashioned cellulose right over the fiberglass. Remember the hole that made the ship sink, well with typical attics the hole would be the exposed edges of the ceiling joists. R-38 in the cavity with R-9.5 or 7.5 for the joists. The hole is the exposed edges. So when blowing the cellulose, keep going until you have a good 4-8″ inches above the edges and you plug the hole ! The added benefit is that cellulose doesn’t suffer at the same rate of r-value loss from the colder temperatures as fiberglass.
Last bullet point above is rafter height. This is also a tough spot to be in, a lot of insulation companies will spray foam in the rafter cavity, right up against the roofs plywood but leave exposed edges of the rafters. So now where is the hole ? If you guessed up top, your right. To make it worse, there is more surface area on a sloped roof than the flat roof below it.
Has your “expert” even measured how much leakage your home has to the attic ? Does he know what the expected yearly savings is from that leakage alone ? I would bet that there is a 95% chance that he doesn’t know. Id bet that there is a 97% chance he wouldn’t know how to.
Lastly, if your home hasn’t been built yet and your doing it from the ground up, remember that current codes require quite a bit of these measures to be addressed already. You shouldn’t have to pay extra for whats required to begin with. You may have to pay a little more to go over and above, but it should sting quite a bit less..
If your considering a Hot roof and comparing it to anything else, make absolutely certain your expert is modeling the overall R values accurately in ALL models. Also make sure
your expert included the 2 additional gable end walls 95% of the roofs have with the equation.
There are many ways to cut costs and guarantee savings. Don’t sing the same music as the Parrots.