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Attic renovation in a “Not-So-Good House”

Andrew Bennett | Posted in General Questions on

My last question was about HVAC and hot water on March 29th 2020.  A few data points to recap.  1900 sq ft house built in the early 1990’s.  Old Aluminum double pane windows, no tyvek under vinyl siding or behind brick on front of house, on crawl space that I am sealing (vinyl vapor barrier brought up the concrete block and adhered via appropriate caulk with taped seams, vents will be sealed, perimeter insulated, and a dehumidifier will be added, and air sealing when I can get back down there to finish), insulation in attic is minimal. 

It is the attic that is the subject of today’s question.  The roof uses a storage truss…but there is no access other than a tiny skuttle hole in my daughters closet.  We also have considerably less space in this house than our last (3200 sq ft down to 1900 sq ft).  We have thrown away, recycled, given away, and minimized…and we still have stuff in our garage.  We want our cars in the garage, not stuff.

Now, I know that Joe “the Gawd of all things building science” says he doesn’t want to see anything in an attic, but insulation.  However, I’m not going to invite Joe over…or if I do I’ll slip him a Valium before he sees my attic.  FYI there is no HVAC ducts or equipment in the attic.

My plan is as follows:
1.  Install a drop down stair in my upstairs hallway.  I know, I know, I can hear you moaning and groaning, but…it is, what it is.
2.  Have what insulation is there removed so I can (or someone else can) thoroughly air seal.
3.  If I have access install some hurricane straps. Tennessee has been hit with too many tornadoes for my taste and I don’t want my roof getting ripped off.  To that end I’d rather seal the roof assembly entirely, but I don’t have the budget to insulate the exterior side of my roof deck.
4.  Install as much insulation as I can at the ceiling with joist height I have in the “storage area” and blow the edges with loose fill.
4.  Use Accuvent cathedral baffles up to the ridge vent, installed so any residual moisture/water makes its way down to the soffit vent.
5.  Install rockwool batt insulation along the roofline (accuvent on the roof side with Certainteed membrain on the interior side).
6.  Possible installation of dehumidifier if need be.

Just to be clear…in the “storage area” of the attic some insulation will be at the ceiling(floor of the attic) and some will be at the roofline.  The area on each side of the storage area will have extra blown in insulation. and there will be a continuous layer of insulation at the roofline from the floor of the attic to the ridge of Rockwool (baffle on the roof side and Certainteed Membrane on the inside (I hope that makes sense).

My thoughts are my “cathedraled” insulation (and possible dehum)will give a bit better weather protection to stuff stored up there than in my garage.  The insulation assembly will be able to dry to both sides.  Our house is near the interstate and the air sealing and rockwool will help with sound (it’s really quite annoying).

Will this work to achieve my goals of:  1.  Creating a storage area with better moisture control than my garage, 2.  A better insulated ceiling/house, 3.  Sound reduction from interstate?

Finally, the bathroom fans and a couple of can lights in the send story ceiling/attic floor.  The fans currently just into the attic.  How do I vent/seal those?  Are there specific bathroom fans that seal better?  How do I deal with the few can lights?

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    When splitting the insulation between the attic floor & roof deck/rafters, only the amount the roof deck counts toward code compliance.

    Be sure that the air barrier on the underside of the roof insulation is truly air tight to limit the stack effect draw of conditioned air from the rooms below into this in-between space.

    Venting bath fans into even a vented attic is a truly BAD idea, and even a code violation in most places. The bath vents need to either extend through the roof, or turn to be side-vented out a wall.

    The can-lights can be replace with surface-mount LED units (preferred), or install a sealed box over them big enough to meet the insulation clearance requirements of the fixture:

    https://s3.amazonaws.com/greenbuildingadvisor.s3.tauntoncloud.com/app/uploads/2018/07/25060105/Air_Seal-Recessed_Attic_Light-1-main.png

    1. Andrew Bennett | | #2

      Thank you for the input!

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