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House remodel, insulation questions

redmonte | Posted in General Questions on

Hi, I have read a ton of the articles and forum posts on this site regarding insulation and conditioned attics. I am currently in the process of renovating a 1960’s 1 story ranch with a full basement on the border between climate zones 5 and 6. I am at the point where I need to figure out my insulation.

The house is gutted to the studs and its going be run off hydronic floor heat in half the house and hydronic ceiling heat in the other half of the house (basement heat is probably going to be radiators or hydonic walls). I have a 4/12 pitch, hip roof with 2×6 rafters. The entire drip edge of the house is vented with several vents along the roof top near the ridge. The house has never had air conditioning and I want to put the air conditioning in the attic because I am not willing to give up any of the already low ceiling height in the basement. I am most likely leaning towards a ductless mini split system or something like the unico system (high velocity ducts).

I have had quotes for high and low density foam and cellulose. I really would like to condition the attic space and airseal it tight but I have a really hard time messing with a system that has been used for a very long time and it works well (unconditioned attic). I have paranoia when it comes to the idea of rotting roof sheathing because of the lack of drying potential if you put foam on the bottom of the sheathing. 

Am I better off blowing in 16″ or so of cellulose after air sealing the attic floor? or should I be looking at closed cell foaming between the rafters? If I do the cellulose, I will be putting baffles in that extend from the space between the roof sheathing and the top plate, up a few feet in the rafter bays to get air flow above the cellulose. The house will have lots of can lights (maybe LED wafer type) and areas where air can make it through the ceiling into the attic space above. Should I be going around with a can of foam and sealing off all these air gaps? Is there a faster way to air seal the entire attic floor? 

Thanks for any input

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  1. user-723121 | | #1

    What is your fuel type? Hydronic heating will likely require a boiler, gas or oil. I do not like the idea of a conditioned attic, this obsession with spray foam has yet to be explained. The very most important part of your project is getting to the highest R-value you can in all areas and concentrating on airtightness. To go through all of the effort of a gut remodel and then needing copious amounts of heat to stay warm is poor planning and execution at it's worst. The formula for a successful project is research, realistic capitalization and hard work.

    You ask the questions and hopefully those well versed in cold climate building can provide some quality insight.

  2. redmonte | | #2

    The previous owners had recently replaced the gas boiler in the house with a nice gas mod con boiler. I took out all the old base board heat as it was an eyesore and I have lived in homes with it before and the ticking noise cannot be avoided with those finned baseboards. I can hopefully avoid the noises pex can make when expanding and contracting.

    Theres no possible way I can get past r-30ish with the closed cell foam in the attic unless I wanted to scab out the rafters which I am not going to do. I was thinking r-60ish of cellulose on the attic floor would do just as well as a foamed ceiling.

    I have performed manual j heat loss calcs and all that stuff so I know that my radiant heat design will output plenty of heat and I am trying to keep the water temps running through the pex sub 100 degrees in winter.

    I dont think the obsession is with spray foam as much as it is air sealing. It just so happens to be that foam is the easiest and fastest (not most economical) way to achieve a tight envelope.

  3. user-1072251 | | #3

    Install minisplits; they heat, cool and dehumidify, and you’ll have 2-3 wall units and one outdoor compressor; nothing in the attic or basement. Air seal the attic floor and pile up cellulose, and where you want more ceiling lights, strap the ceiling and install another layer of drywall (or start by ripping down the old drywall) The newer LED “puck lights” (4 or 6” round) are 1/2” thick and clip to the drywall, so you can install as many lights as you want and not penetrate the air barrier above. One critical thing you did not mention is the basement walls: an 8” concrete wall is R-1; same as a single thick piece of glass; a huge ignored heat loss in most houses, and a good source for internal moisture since concrete is porous and wicks moisture very well from the damp ground to the drier house. 2” polyiso foil is r-13 and helps to keep moisture out of the house and adds greatly to whole house comfort. ‘THERMAX makes a version that is fire rated and can be left exposed.

  4. redmonte | | #4

    Bob, thanks for the ideas. Yes the concrete blocks are 8". I am not planning on finishing the basement quite yet, maybe in a year or so but I am well versed in the rigid insulation required for a proper finished basement. The people that lived here before literally had furring strips ramset in the mortar joints with just 60's panel board up and no insulation of any sort on the slab. When I talked to them after the purchase, they kept reiterating how insanely cold the basement was during the winter, wonder why. House is built on top of a hill and the basement is a walkout and 2 car garage so only 2 walls are "below grade".

    I have never installed a mini split before and I wasnt planning on installing that until next summer. Can the lines for a mini split be fished through a wall easily? I was perhaps thinking of using the ceiling casettes as opposed to the wall mounted unit.

  5. Expert Member
    Akos | | #5

    Since you have an attic, mini split lines are easiest to be fished through there. You can fish it through walls, have to take care not to damage the insulation on it and support it well and allow for thermal movement if a long run. I've also run lines through closet corners, cover with a piece of molding, much easier than through walls.

    If your head is gravity drain, you need to be very carefull with sloping drains, pay attention to keep everything straight and NEVER use those corrugated drain lines.

    Before looking at heads and lines, make sure to check your heat/cooling loads for each room. Typically even the smallest mini split head is WAY over sized for a bedroom creating comfort issues. Better setup is a wall/ceiling/floor unit for larger open areas and a single low profile ducted unit for all the bedrooms.

    Some ducted units can be mounted vertically, you can usually fit it into the back of a closet and keep your ducting out of the attic.

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