Energy Savings from Closed Crawl Space

Here in the Southeast, crawl spaces under houses have always been vented – you’ve seen those louvers around the brick base of houses. Many folks close their vents in the winter to save on heating bills and open them in the summer to prevent mould and mildew. Some folks tarp the ground in the crawl space to prevent excess humidity and push insulation up into the joists for added insulation.

But recently this practice has been re-examined and – what seems like heresy here in humid Virginia – the smart thing to do it completely seal off the crawl space and insulate the exterior walls. A multi-year experiment in North Carolina looked at four new houses build with vented crawl space and eight with closed crawl spaces.

The closed crawl spaces had lower humidity (and no mold problems) and had energy savings of up to 18%. With thick ground tarps, exterior wall insulation, and sealing at the sills (where the brick foundation meets the bottom of the wood frame walls) the crawl space becomes part of the conditioned space of the house. The sealed crawl space has to get some ventilation from the house above and this air has to be vented to the outside with a one-way vent.

The advantages for energy savings are running the duct work through conditioned space, meaning less heat exchange with the air, and having an insulated space below the house that keeps close to the temperature of the house.

So we decided to go with a conditioned crawl space and used the Drying Company in Williamsburg familiar with the practice. The City of Norfolk was a little non-plussed by this but Nick Shawyer went on line and found the building code specs which we provided to the City and they approved the plan.

The framers then used a strip of closed cell foam to separate the wood sill from the cinderblock and then caulked the joists as they went on the block, to complete the seal.

Insulated exterior walls and sealing the sill

One warning – if you are in a flood plain you will need to put flood vents, since FEMA requires vented crawl spaces to prevent water pressure from the outside of the foundation from building up and collapsing the foundation walls from flood waters. You will need to double check this with FEMA and the city – see the York County code mentioned below.

CRAWL SPACE REFERENCES

BUILDING CODE SPECS FOR CLOSED CRAWL SPACE

SAMPLE FLOOD ZONE CODE – YORK COUNTY

Energy Issues – Step one

Energy issues are coming up on top of the list to deal with first, since this is the big carbon footprint item – 50 to 70% of a home’s energy goes toward heating and cooling. Another DOE statistic is that 40% of a home’s energy is lost due to air infiltration.

Michigan Technical University put out a graph of home air leaks and their sources…

The top offender is a poorly sealed and insulated house envelope – certainly an issue in a 92 year-old house with no insulation and lots of gaps. With the advantage of having the walls opened to the outside sheathing, the answer seems to be to blow in foam insulation to seal the house and insulate it at the same time.

Closed cell versus open cell spray foam?

Closed cell gives you a vapor barrier, more insulation per inch of foam (R=6), and some structural benefits. Open cell foam has lower insulation per inch (R=3.5), is more permeable, but is much cheaper. Closed cell foam has been using HCFC carriers (bad for the ozone layer and being phased out) while open cell foam uses water as an installation carrier. However, there are now bio-based closed cell foams that use water in place of HCFC’s.

Additional Expense with Closed Cell Foam

In the end, we went with a 2″ layer of closed cell foam on the entire house – from roof peak to foundation.  We had the old foundation sealed along the sill (see next post).  Then we came in with cellulose insulation on the non-brick walls (second story on old house and all of the new construction), and in between the rafters in the roof.

BUT…this meant we had to replace all the old windows, since the sash weights won’t work with all the foam in the walls.  This was expensive – about $10,000 in windows, about 20 of which were replacement in the old house (the new house windows would have been required anyway).  We went with standard sized Anderson dual pane, windows and then sealed them up.  In the end, this is going to give us better performance, but it is something to consider in an existing house – the old windows will have to go with wall insulation.

Tyvek variable?

As an additional variable, the existing structure will probably have its cedar shingles removed and replaced by HardiShingles (the cedar shingles proved to be such fuel for the fire – we do not want to have them around). During the process of removing and installing shingles, the house can be wraped with Tyvek, providing a 30% reduction in air infiltration. Is this enough to go with open cell foam rather than closed and get the money savings?

Turns out when we took the shingles off part of the house (burn damage) and took the cedar shakes off, there were too many gaps in the sheathing.  The old 1X6 planks had large gaps that would result in shingles not being nailed down.  So we had to sheath the WHOLE upstairs and roof in OSB sheets.  That was wrapped in Tyvek and then the HardiShingles and light colored shingles were nailed down.

The trick is to get a good Heating Contractor who will work with you throughout the process, adjusting along the way, testing, advising. We interviewed four contractors, playing dumb and greedy.  Many of the “Green” contractors just want the green in your pocket.  We finally found a great HVAC contractor in the Virginia Service Company.

They went through the house, room-by-room, to figure out the heating and cooling load.  We reduced the capacity with the plans for super-insulating the house.

But after wrapping the house, sealing the envelope with foam, and replacing the windows do we seal so much that we have a ventilation problem?  YES.

Ventilation?

As you tighten up the envelope to eliminate air infiltration your eliminate….air infiltration. If it falls below the minimum needed for your house and family size, you will need to adapt by putting in home ventilation systems.

The reasons are many – air quality deteriorates as the normal (and not so normal) airborne compounds in your house recirculate. Water vapor is problem in this part of the county and mold is a major issue. Ventilating bathrooms and oven areas is one way of dealing with this on a spot basis, but a more complete system in recommended if you tighten up your house.

How much airflow do you need? According to the standards put in place by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) in 2003, the new ventilation standard for residences- ASHRAE 62.2 you need to compute how many cubic feet per minute (CFM) you need. The equation is (cfm) = 0.01 X your floor area + 7.5 X (your number of bedrooms plus 1) Another way of getting at this is to plan for 0.35 air changes in the house per hour or 15 cfm per person, whichever is greater.

So in our case, we are looking at about 60 cfm in ventilation.  We went with a heat-recovery system and electrostatic filters.  It was about $2,000 but for a family with allergies in a region full of pollen, this system makes lots of sense.

Resources

Southface in Atlanta – http://southface.org/

Fact Sheets (including one on whole building ventilation) http://southface.org/web/resources&services/publications/factsheets/sf_factsheet-menu.htm

Built Green – Home Builders of Greater Denver Colorado – http://www.builtgreen.org/default.htm

Built Green Home Ventilation

http://www.builtgreen.org/articles/0411_Home_ventilation.htm

Getting Started on the Project: Planning

The first step in planning a green remodeling project is to list all the options for reducing the energy/water/greenhouse gas footprint of the structure. Templates for this process can be found on the Web at a number of places. One great resource is the Portland, Oregon Office of Sustainability downloadable Guidebook site, specifically, the “Green Home Remodeling Guide.” Another is the Seattle Department of Planning and Development’s City Green Building site.

The basic list looks like this:

Design and construction planning

■ Salvage Reusable Building Materials

■ Recycle Job Site Construction and Demolition Waste

■ Use Salvage Materials

■ Use Recycled-Content Materials

Site work

■ Install Permeable Paving

■ Install Rainwater Harvesting

Foundations

■ Incorporate Recycled Fly Ash in Concrete

■ Reuse Form Boards

■ Use Recycled-content Rubble for Backfill Drainage

■ Use Aluminum Forms

■ Install Rigid Foam Insulated Concrete Forms (ICFs)

Structure

■ Substitute Engineered Lumber for Solid Sawn Lumber

■ Use FSC-Certified Wood for Framing

■ Use Wood I-Joists for Floors and Ceilings

■ Use Structural Insulated Panels (SIPs) for Walls / Roof

■ Use Salvage Lumber

Exterior finish

■ Use Sustainable Decking Materials

■ Use Treated Wood that Does Not Contain Chromium or Arsenic

for Decking and Sill Plates

■ Use Fiber-Cement Exterior Siding

Plumbing

■ Install Water-Heater Jacket Insulation

■ Install a Tankless Water Heater

■ Insulate Hot and Cold Water Pipes

■ Retrofit all Faucets and Showers

■ Replace Toilets with Low Flow Models

■ Install Chlorine Filter on Showerhead

■ Install Water Filtration Unit at Faucet

Electrical

■ Install Compact Fluorescent Light Bulbs

■ Install Lighting Controls

Roofing

■ Select Light-Colored Roofing

■ Select Safe and Durable Roofing Materials

Appliances

■ Install Energy-Efficient Refrigerator

■ Install Water- and Energy-Efficient Dishwasher

■ Install Horizontal Axis Washing Machine

Insulation

■ Upgrade Wall and Ceiling Insulation

■ Install Recycled-Content, Formaldehyde-Free Fiberglass

Insulation

■ Use Cellulose Insulation

■ Reduce Air Infiltration

Windows

■ Install Energy-Efficient Windows

Heating, ventilation and air conditioning

(HVAC)

■ Use Duct Mastic on All Duct Joints

■ Install New Ductwork within Conditioned Space

■ Install 90% or Greater Efficiency Gas Forced Air Furnace

■ Install Zoned,Hydronic, Radiant Heating

■ Vent Range Hood to the Outside

■ Install Solar Attic Fan

■ Clean All Ducts Before Occupancy

■ Install Whole-House Cooling Fan

■ Retrofit Wood-Burning Fireplaces

■ Install/Replace Dampers on Fireplaces

■ Install Airtight Doors on Fireplaces

■ Install Heat Recovery Ventilation Unit (HRV)

■ Install Separate Garage Exhaust Fan

■ Install Effective Bathroom Fans

Renewable and solar energy

■ Incorporate Natural Cooling

■ Incorporate Passive Solar Heating

■ Install Solar Water System

■ Pre-Plumb for Solar Water Heating

■ Install Photovoltaic (PV) Panels

Indoor air quality/finishes

■ Use Low/No-VOC and Formaldehyde-Free Paint

■ Use Solvent-Free Adhesives

■ Use Low-VOC,Water-Based Wood Finishes

■ Substitute Particleboard with Formaldehyde-Free Materials

■ Use Exterior-Grade Plywood for Interior Uses

■ Select Formaldehyde-Free Medium Density Fiberboard (MDF)

Flooring

■ Select FSC-Certified Wood Flooring

■ Use Rapidly Renewable Flooring Materials

■ Use Recycled-Content Ceramic Tile

■ Use Exposed Concrete as Finish Floor

■ Replace Vinyl Flooring with Natural Linoleum

■ Install Recycled-Content Carpet and Cushion

Given the nature of our situation – existing house burned out – some of this does not work, such as salvaging materials on site. While waiting for our insurance process, we began planning with the biggest need – making a 1916 house with no insulation more energy efficient.

Green phoenix from the ashes of our house

We [Margie Mulholland and Skip Stiles - with Maeve (~6) and Patrick (~3)] had a major house fire on November 5th in our wonderful 1916 house near downtown Norfolk, VA. The house is a mess and we will be out of it for at least 8 months. To remove the smoke damage, they have to take EVERY wall and ceiling in EVERY room down to the studs and rafters.

The silver…..rather green…..lining to all of this is the opportunity to redevelop a 1916 house to fit 2016 standards for energy and water use and current concerns about climate change and greenhouse gas emissions. That is what this blog is about – a diary and open discussion about our efforts to redevelop our lovely house and get a green phoenix to rise from the ashes.

We are partnering with Nick Shawyer of DesignBuildIt. Nick has been developing a “green” redesign/remodeling approach in Norfolk, a 400 year-old, built-out area in which the existing housing stock will be around for decades to come. Unlike new construction areas in the region, the older parts of Hampton Roads (Norfolk, Portsmouth, Hampton, Newport News – the “First Cities” of Hampton Roads) will have to deal with energy and water conservation and greenhouse gas (GHG) reductions through redesign and retrofitting. Shawyer has begun working new ideas into old houses, starting with the 1898 Larchmont farm house he lives in and on which we partnered in the redevelopment.

At the start of this project, we decided to try to do as much “green” and LEED compliant as we could, given the situation and budget we were working under. We met with Rob Berz of the Hampton Roads Green Building Council for advice. He visited our burned house and made lots of suggestions – starting with documenting everything and listing all of the options under consideration. That is the first step we are taking now.