Month: April 2021

A: Hi XXXXX, spray foam has R5 insulation per inch whereas fiberglass is R3, so in that sense spray foam is more efficient.
However, spray foam sticks to the joists like glue (that’s the idea) so you can’t get it out if you need to get access to a pipe or wire. For this reason I do not recommend spray foam for the ceiling of a basement. 
Also, spray foam is more expensive per inch and per R value than fiberglass. So, economically, sprayfoam is less efficient than fiberglass. 
And, finally, the gas used to blow the bubbles in spray foam is 1,000 times more potent than CO2 at causing global warming. 
And, finally finally, spray foam is flammable whereas fiberglass is not. 
For all these reasons, I prefer fiberglass to spray foam for insulating the ceiling of a basement. 

And, really finally, fiberglass is porous to air which means that if some water does get into the fiberglass (like from an overflowing bath) it will evaporate and dry out. Spray foam is water tight which means any water falling onto the spray foam from above will sit there like a puddle with no ventilation and hence will take much longer to evaporate and dry out. This is risk for mold, rot and asthma for the people in the house.

A: Correct. Go to the top of the class. If you use the basement as living space, you need to insulate the walls and the floor of the basement.

A: We did not. It is almost impossible to seal an existing house so well that it gets stuffy and needs mechanical ventilation. However, on tightly sealed new construction you really do need one, it is not an option.

A: Yes, this is a good idea – insulate the basement ceiling where you don’t mind the basement getting a few degrees colder. If the basemetn space is living space then it is better to not insulate the basement but instead insulate the walls and add a thick carpet with a thick underlay pad.

A: I think standing-seam metal roofs are the best long-term investment for making a roof. They play especially well with solar panels because the panels are clamped to the seams, so no penetration is required on a sloped roof. 

A: Insulating contractors I have spoken with recommend removing the insulation on the floor before adding insulation to the sloped sides of a roof. This makes sense if the insulation has mold growing or has mice living in it.  But other than that, I do not see what harm in having more insulation. Often, the reason people are insulating the sloped sides of a roof when the floor of the attic is already insulated is because they are adding a heat pump air handler unit to the attic. It is essential to insulate the sloped parts of a roof when adding an air-handler unit to an attic or the heat from the air handler in winter will melt the snow and cause icicles or ice dams. The only circumstance that I could see that would warrant removing the insulation on the floor would be if the attic now gets warmer in winter than the house below it. Then it would make sense to allow the heat from the air handler to be conducted down into the house. These circumstances would be quite likely if you were adding a very thick layer of spray foam to the sloped parts of the attic. 

A: If you replace the roof, you can add a layer (or two) of ISO board to the roof on the outside of the plywood sheathing. This is what we did on our flat roof. The DOE recommends that roofs be insulated to at least R49 in MA. This would require 5 layers of ISO board. In my opinion this is spending too much money given how much you can save – insulation has diminishing returns to investment. After about R35-R40 the savings from the next layer of insulation rarely pay for the extra cost. Spend the money you save on a good air-sealing job.

A: The easiest way to reassure yourself about indoor air quality is to measure it using an inexpensive indoor air quality monitor. Ours is from Foobot but there are many others. Our indoor air quality is consistently excellent. Our insulation is a mixture of fiberglass and ISO board panels which are essentially spray foam in a board. I do not know of any indoor air quality issues arising from any of the common types of insulation like fiberglass, cellulose, spray foam, ISO board or rockwool. Concerns over off-gassing from insulation usually relate to urea formaldehyde foam insulation. The use of this was banned in the USA in 1982.

A: If the basement space is used as living space (and heated) then there is no need to insulate the ceiling if the walls are already insulated. It will be better to just install a thick pad under the carpet – and that will keep your feet warmer too! If the basement is not used as living space and is unheated then it makes good sense to insulate the ceiling so that you are not waseting your heat on your luggage.

A: You could replace the hot water heater with a heat-pump hot water heater, replace your AC unit with a heat pump for heating the house and leave your gas boiler in place for heating the house on bitterly cold winter days.