Maximizing home comfort – The roof crawlspace insulation advantage
In most Washington DC buildings, there will be a little bit of space between the top floor ceiling and the underside of the roof membrane. In the case of the photo below, you can see the picture of a man crawling inside of an attic crawl space. That added crawl space only allows for about 24″ of clear space between the top of the top floor ceiling joist and the underside of the roof rafter at the top of the crawl space. It’s somewhat tight to move around and work in a crawlspace, but the space can still be accomodsting enough to allow for additional convenience in maintenance in insulation.
The crawlspace has a few useful purposes, some examples follow below.
1. Crawlspaces allow for the sloped angle of the roof, required to shed water naturally, by gravity to not be transposed to the interior ceiling below. Essentially, since there is a finished ceiling below which is flat, the triangle shape of the attic can allow for a sloped roof at the top with a flat ceiling at the bottom. Because of this variation, you don’t see the slope from the interior space of the building.
2. Rooftops sit in the sun in the summer largely unprotected from sunlight, generally outside of shade. Rooftops can become extremely hot. A properly built attic crawlspace area can allow for cross ventilation so that hot or heating air in the crawlspace we’ll rise to a upper vent area and and cooler outside air will naturally be drafted in through the lower area in what is called the stack effect.
3. As most historic homes have been at least slightly renovated or modified over the years, the rooftop crawlspace or attic allows a good space to install do install mechanical or HVAC ductwork or modern electrical systems building. This explanation doesn’t give reason for the original construction but it is a good reason not to remove crawlspaces now and convert them to vaulted ceilings in modern times.
4. Insulation. The attic crawlspace is a perfect place to add onsulation. In the photograph above you can see that yellow fiberglass batt insulation has been added to the ceiling joist bay area. This installation probably has between approximately R-30 and R-38 thermal resistance. That amount of insulation is less than what is required by modern building code in many locations, but that amount of insulation still has a significant effect in reducing the energy used for heating and cooling in the is the winter and summer, respectively.
5. Storage space. This thin and narrow space is largely uncomfortable and restrictively small to be very useful, but still once in a while, for certain items that only need to come in-and-out of storage very rarely, this space can actually be useful. It’s wise to not store anything in the attic that can be damaged from exposure to very high temperatures.
