At what climate does each envelope upgrade start to pay, when climate is a continuous axis?

What it found

Makes heating and cooling degree-days the axis of house-energy’s 640-package net-present-cost search and finds each upgrade’s exact switch-on point. With a gas furnace and 500 cooling degree-days, slab-edge R-10 pays from 3,271 heating degree-days, an R-30 attic from 4,029, 5 ACH50 from 4,485, 3 ACH50 from 5,769 and an R-38 attic from 8,368; a heat pump lowers each of the first four by about 27% (2,386 to 4,209). Cooling switches on only the attic and air sealing, above about 3,000 cooling degree-days; windows never leave U 0.50. The slab-edge threshold falls exactly in proportion to the energy price. Stylised: house-energy’s unsourced prices, degree-day loads and no solar gain.

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

More in Open-source residential construction

• How much extra can a tight envelope cost before it stops paying back on a 480 sq ft backyard cottage?How much extra can a tight envelope cost before it stops paying back on a 480 sq ft backyard cottage? The ADU's whole upgrade package can carry $1,409 to $3,104 of extra first cost (3% real rate, heat pump); at assumed prices only the wall switch clearly pays. Stylised.
• Does a tighter envelope let a 480 sq ft backyard cottage use a smaller heat pump, and is the saving worth counting?Does a tighter envelope let a 480 sq ft backyard cottage use a smaller heat pump? The tight package cuts the design heating load about 36.5%, worth a $450 to $1,800 equipment step credit (assumed catalogue and prices) that nearly closes the payback gap of the costed upgrades in three colder climates. Stylised.
• When does cooling, not heating, set the heat pump size for a 480 sq ft backyard cottage?When does cooling, not heating, set the heat pump size for a 480 sq ft backyard cottage? Adding a summer load (conduction, window solar gain, internal gains) shows cooling governs only in Houston (12 kBtu/h baseline, 9 tight); sizes and credits elsewhere are unchanged, and Houston's credit swings between $0 and $900 with SHGC and latent allowance (stylised, assumed inputs).
• How much lumber does a prefabricated roof truss save over rafters and ceiling joists?How much lumber does a prefabricated roof truss save over rafters and ceiling joists? A pin-jointed W truss with NDS checks uses 40-55% less nominal lumber per sq ft of plan than 16 in rafters plus ceiling joists over 12-30 ft spans at 30 psf snow (stylised: no plates, bracing or heel details).
• When does building a house's wall shell in a factory beat building it on site?When does building a house's wall shell in a factory beat building it on site? Panel layout, sheathing nesting (1 sheet in 33 saved) and a Monte Carlo of the shell: panelised takes 2.17 d against 1.96 d on site and costs 38% more at assumed rates; it is faster only from about 58 ft long. Closed panels (insulation, wiring, windows built in) cut the gap: cost parity at a factory labour ratio of about 0.45 and a day saved. Stylised, every rate assumed.
• Which foundation is cheapest for a small house as the frost line gets deeper?Which foundation is cheapest for a small house as the frost line deepens? At 48 in frost a frost-protected shallow foundation is $13.2k against $20.6k slab, $24.1k crawlspace and $54.9k basement in a stylised model.

All 41 Open-source residential construction projects →

Other research topics

Proper scoring & elicitation28Effort & peer prediction9Verification games & slashing19Detection & tolerances14Markets as routers13Prediction-market design9Paying contributors8Decentralised training systems23Digital twins & sim-to-real164LLM chip design loops40Robot manufacturing loops53Ambient AI assistant46Self-replicating manufacturing34Simulation-first design64Engineered clothing45Task-specific AI accelerators40Algorithmic chip-design loops42Open-source purpose-built robots44The software-engineering loop43Adversarial human imitation41Open-source residential construction41Autonomous multi-angle capture34Sensing, imaging and 3D31Energy supply and dense energy storage39Robot societies among people31Agentic co-design of low-cost robots27Laundry-hanging robots25Machine learning on qualitative data23Robots on the building site27Civilizations & group psychology1History & human sciences1

Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.