I presently thinking about using the SprayFoam insulation in a new home that I am building. My home will be heated by natural gas so I will have natural gas piping running into the attic space. In my attic I will have, 2 natural gas HVAC units & a natural gas tankless water heater. My General Contractor has been asked, since this house will be virtually an envelope once the insulation is installed and the attic will be sealed, how will the attic area ventilate if there is a natural gas leak. The people who are questioning this, are concerned that a natural gas leak will form a gas pocket that could be ignited by the 2 HVAC units or tankless waterheater. Since Spray Foam insulation if fairly new to him & the construction board that he sits on, they are not to up to date on the material and what needs to be done to eliminate such issues. Have you run into this question before and what do you suggest.. Thanks

You might check code. I put my gas water heater in the garage for this very reason. I also went with geothermal to eliminate gas in the closed attic. I added an ERV for fresh air -- connected to the bathrooms. However, i believe there are ways to ensure proper venting.

If geothermal sounds like an option but seems too expensive. You can usually reduce your tonnage by as much as 50% if you use ICF and foam the attic. If your in LA ICF might be a good idea anyway.

Thanks for the info. I had 2 ICF companies contact me and they are recommending installing a small ERV unit to remove any gas buildups. I have also did some research, I can have natural gas sensors installed in my attic that will connect to my security system which will pick up low levels of natural/metane gas. Thanks again.

Better check the IBC, I read that any foam placed in crawlspaces or areas with sevice entrances needs to be fire coated. Maybe someone knows if this is true. I will try to find the place where I read this.

You'll definitly need HRV/ERV for any super-tight house. (In humid LA, ERV is preferable, since it lowers the latent AC load of the ventilation air whereas HRVs do not.)

Combustion appliances should all be direct-vent/sealed combustion as well, since you'd be required to put large holes in your thermal & pressure envelope to guarantee combustion air. This would also keep the appliance from lighting off a gas leak as well.

Gas sensors are always a good idea when you have gas plumbing in your house no matter how well ventilated.

IIRC, if there is no air communication with the crawlspace and no ignition sources, the thermal barrier requirements for foam insulation are relaxed in the IBC from 1/2" gypsum to some lesser level, and some locations make exceptions altogether for truly dead spaces with only service & inspection hatches. But if there are any ventilation ducts in the space it reverts to the 1/2" requirement. In LA crawlspaces in supertight houses may become humidity traps, and a small amount of active ventilation into that space would be recommended, so bottom line, count on applying a thermal barrier in this instance.

Lakajun, I take it the people asking this question have never had a house with gas heat, fireplace, dryer and/or range. Gas pipes run throughout many homes with no ventilation "in case it leaks".