Spray Foam Insulation in MA | Attic/Roof deck insulating saves on Summer cooling costs
The benefits of insulating attics is not only vital to reducing energy use and costs in the cold Winter months. It is the most important step to reducing cooling costs in the hot, Summer months.
So should you add significant amounts of blown cellulose to the attic floor? Or, spray foam insulation between the rafters on the roof deck?
It depends on whether you have heating/AC units in the attic or other appliances and whether you want to gain the effects of air-sealing. It also depends on whether you want to prevent ice damming in the Winter and extend the life of your roof.
The location of the thermal barrier is really the major question here. If you insulate just the attic floor then the attic itself is not an insulated space. You are boxing in the home below the attic and leaving the attic uninsulated and unconditioned. So why does that matter?
In some cases it really does not matter. Having no heating/AC units in the attic, no major appliances, little concern for the affect of temperature on stored items in the attic, no ice dams in the winter and have an efficiently designed roof means you are the perfect candidate for blowing in cellulose on the attic floor or installing fiberglass in the same way. (Installing fiberglass in the attic requires you to have some form of ventilation because fiberglass needs to breath to be effective. Typically soffitt vents, a ridge vent and baffles are used to solve this problem. Cellulose does not require breathing.)
However, if you do have heating/AC units located in the attic along with ductwork you should consider making the attic itself a conditioned space to increase the efficiency of these units/systems by spraying foam insulation between the rafters of the roof deck.
Other benefits of adding spray foam to the underside of your roof:
Air sealing benefits. Above and beyond R-values, an airtight attic is essential to conditioning of you whole house.
Ice dams. By insulating directly onto the underside of your roof you will experience significantly less or eliminate ice dams during the winter. Ice dams are caused by unnatural melting of roof snow/ice due to the escape of heat from your home causing the water to refreeze when it reaches the overhangs/eaves.
Many shingle companies say that spraying foam on your roof deck will reduce the life of the shingles and they sometimes use this as an excuse to void a warranty. It is just not true. Studies have shown that spraying closed-cell foam insulation in an attic can extend the life of your roof by up to 30%.
Hopefully by now you have a better understanding about the different ways of insulating your attic. Visit http://greenbearinnovations.com for more information about our products and services.
Please note that when sealing and attic space we recommend installing an HRV system to ensure that moisture build up is eliminated and that stagnant air is being exponged and replaced with fresh, conditioned ai Even duringr.
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June 17th, 2009 at 10:19 pm
You don’t address the fact that if you spray the underside of the attic, you are adding to the load of the HVAC unit(s) of conditioned space in the attic. Is that fully offset by the ability to be air tight? And also, compared to insulation on the floor of an attic, how does the foam hold up to the 160+ degree heat of a roof compared to the 130 degree air temperature of an attic when insulation is on the attic floor?
June 17th, 2009 at 11:55 pm
Although the sprayed roof deck is considered the thermal barrier in cases of new construction using spray foam there we would always recommend ample insulation on the attic floor for a dual benefit. The cost of adding ten or more inches of blown cellulose is worth the small price. Adding SPF under the roof deck will not only assist you in conditioning the attic space but will eliminate ice dams, prolong the life of HVAC units located in the attic, etc.
Clients that want to use the attic as a conditioned space do not necessarily have to heat and cool the space therefore adding to the HVAC load. That assumption is incorrect. By insulating the roof deck we are reducing the conductive heat from the sun bearing down onto the roof and eliminating cold drafts that typically keep an attic 20 or more degrees cooler in the winter months here in New England.
Entering an attic insulated on the floor with R-50 in July is virtually unbearable. An HVAC unit located in this space will struggle and be VERY energy inefficient, reminding you that in NE many HVAC units are placed in the attic. By conditioning the floors below at a normal temperature of 70 degrees in the summer and by adding an R-30 or more of SPF on the roof deck, the attic space will not typically exceed 80 degrees. So instead of an HVAC unit struglling to cool an entire house while running at a 160 degree operating temp, it will efficiently operate at a comfortable 80 degrees and save the homeowner boat loads of utility costs.
To summarize, the load of the HVAC systems located in the attic itself will be greatly reduced. If the attic is already used regularly for traffic, storage and rooming then the thermal barrier should be the roof deck and not the attic floor. The opening and closing of attic stairs with regular traffic can boost a utility bill by 10% if it is unconditioned. If finishing an attic for rooms, most homeowners will run HVAC up there anyways so why not insulate it properly. The foam holds up great at 160 degree heat and will typically keep an attic around 80 degrees without any A/C with and R-30 or greater of SPF.
Should you have any other questions or concerns feel free to give us a shout. We are always glad to answer questions and concerns of consumers.
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