Welcome to the Fine Homebuilding podcast, our weekly discussion of building, remodeling, and design topics aimed at anybody who cares deeply about the craft and science of working on houses. This is senior editor Patrick McCombe. I’m joined by Fine Homebuilding editorial director Brian Pontolilo, production manager and FHB contributing editor Ian Schwandt, and producer Andres Samaniego. Please email us your questions to [email protected].

You can find previous podcasts and check out the show notes at finehomebuilding.com/podcast

Check in:

Ian: Shop improvements

Brian: FHB Summit September 18^th and 19^th

Andres: Finishing pressure-treated lumber

Patrick: BS* & Beer Seattle

Feedback 1:

Adam from Chittenango writes:

Hello FHB Podcast,

I thought you might be interested in knowing that Scouting America (formerly Boy Scouts but now co-ed) is still promoting the skilled trades. It would be interesting to see if a partnership between TradesUp (formerly Touch a Trade) and Scouts could help reach a broader audience. You can find details here.

Question 1: Can I use a slab foundation for radiant cooling for the building? And how should I deal with radon mitigation in a tight slab-on-grade house with continuous insulation?

Erik writes:

Hello FHB Crew!

I’m currently in the very early planning stages of a new build in central Wisconsin (climate zone 6a). I’ve recently purchased 3.4 acres and am planning to start building a 50-ft. x 81-ft. barndominum-style home and shop. Why a barndo? I can get a kit for the base structure for less than $40,000… And I watch a lot of RR Buildings on YouTube 🤣. I’m convinced I can build to high-performance standards. I will be the GC and do as much of the work as possible myself.

Roughly half of the building will be house and the other half shop space and mechanicals. It will be slab on grade, and there will be a proper foundation/footers, with the posts bracketed on top of the foundation walls. I’m going to sheathe with ZIP (possibly ZIP R-Sheathing) for WRB and air tightness with Comfortboard and Rockwool in the wall cavities.

The cross section of the wall as I imagine it from the outside in is: metal siding; ZIP sheathing; exterior girds with Comfortboard between the empty vertical spaces; 6-in. posts with Rockwool between them; a one-way vapor barrier similar to SIGA Majrex (that lets vapor into the envelope for removal via HVAC but not into the walls); and, finally, another layer of interior girds with Comfortboard between them. I’m still thinking on how what I want for the roof insulation, so that’s for another future email 😀.

I have a million questions, but I’ll only ask two(ish) in this email.

My current plan is to install via an air-to-water heat pump. I’m wondering if I can also use the slab for radiant cooling for the building? I am planning on having an ERV, a whole-building dehumidifier, and a makeup air system for proper ventilation. Has anyone seen a slab used for cooling like this? The biggest downside I see is potential condensation forming in the slab. My backup plan would be to use hydronic radiant panels for cooling.

My other question is how to deal with radon mitigation in a tight slab-on-grade house with continuous insulation? Does a properly applied continuous insulation under the slab also make the home airtight from the bottom? Since there will be gravel under the slab, can I just have several suction points with 4-in. PVC around the building going through the slab/foam board/vapor barrier?

Thank you for great podcast. I’ve been listening for years. I love the banter and I hope you can address this on the show so I can be famous-adjacent 🤣.

Erik N

RELATED STORIES

• GBA.com: Cooling with Radiant Tubing
• GBA.com: Radiant Heating and Cooling
• Placing and Finishing a Heated Concrete Floor
• Radon Mitigation with Interior Perimeter Drains
• Reliable Radon Readings

Question 2: Do you need dedicated ductwork with an ERV?

Spenser writes:

Hey guys,

My wife and I are a young couple building our first home in Michigan. Here are the details of the home:

• Ranch (3 bed, 2 bath)
• Slab-on-grade (1600 sq.ft.)
• 6/12 shingled, vented roof
• 2×6 exterior walls
• 9-ft. flat ceilings
• Zip system wall sheathing
• Radiant in-floor heating
• Multihead minisplit system

We were planning on closed-cell foam/cellulose damp spray for wall insulation and blown-in cellulose for the ceiling.

We have recently been learning more and more about building science and now realize that our current heating/cooling design has some drawbacks when it comes to bringing in fresh air and filtering out stale, humid indoor air (considering there isn’t a dedicated duct system).

We question if we need an ERV? If we do, where should we place the ductwork for it, considering it will have a traditional vented roof and no basement? Can insulated flex ducts run on the floor of the attic then be buried with the attic insulation? Do we build bulkheads to hide them, or go for the industrial look with exposed ductwork? We realize now that we should’ve learned about how our home’s HVAC systems will operate before starting to build, but here we are.

Spencer

RELATED STORIES

• Choosing Between HRVs and ERVs
• Running Ducting for an ERV
• HVAC Design for a Tight House
• VIDEO: Principles of Residential Ventilation
• Ducts for HRVs and ERVs
• Plenum Trusses for Slab-on Grade Construction

Sign Up for an All-Access Membership

Unfortunately that is all the time we have for today. Thanks to Ian, Brian, and Andres for joining me and thanks to all of you for listening. Remember to send us your questions and suggestions to [email protected] and please like, comment, or review us no matter how you’re listening–it helps other folks find our podcast.

Happy Building!

Fine Homebuilding Recommended Products

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

8067 All-Weather Flashing Tape

Available in 2- to 12-in. widths, this is a good general-purpose flashing tape that sticks well to most things. It features a two-piece release paper, water-shedding layers, and good UV resistance.

Buy at Amazon

Reliable Crimp Connectors

These reliable, high-quality connectors from Wirefy work on 10-22-gauge wire have heat-shrink insulation to keep out water and road salt.

Buy at Amazon

Handy Heat Gun

This heat gun is great for drying joint compound, primer and paint when patching drywall and plaster walls. Plus it can soften adhesive, get a very cold small engine to start, and shrink heat-shrink tubing.

Buy at Amazon