Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
EXTERIORS of BUILDINGS
ADHESIVES, EXTERIOR CONSTRUCTION
AGE of a BUILDING - how to determine
ALGAE, FUNGUS, LICHENS, MOSS
ARCHITECTURE & BUILDING COMPONENT ID
ATTIC CONDENSATION CAUSE & CURE
BEST CONSTRUCTION PRACTICES GUIDE
BRICK VENEER WALL Loose, Bulged
BRICK WALL DRAINAGE WEEP HOLES
BOOKSTORE - EXTERIORS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
DECK & PORCH CONSTRUCTION
DECK COLLAPSE Case Study
DECK FINISHES COATINGS PRESERVATIVES
DECK FLASHING LEAKS, ROT Case Study
DEFINITIONS of ENGINEERED WOOD OSB LVL etc
DRYWELLS, FRENCH DRAINS for FLAT SITES
EARTHQUAKE DAMAGED FOUNDATIONS
EIFS & STUCCO EXTERIORS
ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY
EXTERIOR WALL SIDING TRIM & FINISHES
FIBERGLASS INSULATION MOLD
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FRAMING METAL STUD PERFORMANCE
HEAT TAPES & CABLES for ROOF ICE DAMS
HOUSEWRAP AIR & VAPOR BARRIERS
KIT HOMES, Aladdin, Sears, Wards, Others
LEAD POISONING HAZARDS GUIDE
LEAD PAINT REMOVAL ALTERNATIVES
LEAD PAINT REMOVAL TROUBLES
LEAD PIPES in BUILDINGS
LEAD in ROOFING, EFFECTS
LEAD TEST KIT for HOME USE
LEED GREEN BUILDING CERTIFICATION
LOG HOME GUIDE
MOISTURE CONTROL in BUILDINGS
MOLD DETECTION & INSPECTION GUIDE
MVOCs & MOLDY MUSTY ODORS
ODORS GASES SMELLS, DIAGNOSIS & CURE
PAINT ANALYSIS, DIAGNOSTIC USES
PAINT & STAIN GUIDE, EXTERIOR
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
PAINT FAILURE CHECKLIST
PORCHES & Sunrooms
PORCH CONSTRUCTION & SCREENING
SHEATHING, GYPSUM BOARD
FIBERBOARD SHEATHING, Celotex Homasote & Other
SHEATHING, FOIL FACED - VENTS
SIDING TYPES, INSTALLATION, DEFECTS
SIDING, ASBESTOS CEMENT
SIDING ASPHALT ROOF SHINGLES on WALLS
SIDING ASPHALT SHINGLE or SHEET
SIDING DAMAGE by SPLASHBACK
SIDING EIFS & STUCCO
SIDING, FIBER CEMENT
SIDING, WOOD PRODUCT CHOICES
SIDING, WOOD INSTALLATION
SIDING WOOD, FAILURES OVER FOAM BOARD
SIDING WOOD, FLASHING DETAILS
SIDING WOOD SHINGLE INSTALLATION
STAIN & BIODETERIORATION AGENT CATALOG
STAINS on & in BUILDINGS, CAUSES & CURES
STAINS on CONCRETE
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIN DIAGNOSIS on BUILDING INTERIORS
STAINS & FINISHES, INTERIOR
STAIRS, RAILINGS, LANDINGS, RAMPS
STONE SURFACE CLEANING METHODS
STONE VENEER WALLS
STRAW BALE CONSTRUCTION
STUCCO WAll FAILURES DUE TO WEATHER
STUCCO WALL METHODS & INSTALLATION
STUCCO OVER FOAM INSULATION
STUCCO PAINT FAILURES
SURFACE GRADING, SITE DRAINAGE
TEST KITS for DUST, MOLD, PARTICLE TESTS
THERMAL EXPANSION CRACKS in BRICK
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL IMAGING MOLD SCANS
THERMAL MASS in BUILDINGS
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VENTILATION in BUILDINGS
VINYL CHLORIDE HEALTH INFO
VINYL SIDING or WINDOW PLASTIC ODORS
VOCs VOLATILE ORGANIC COMPOUNDS
WALL FINISHES INTERIOR
WALL CONSTRUCTION BARRIER vs CAVITY
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in BUILDINGS
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
WIND WASHING INSULATION At EAVES
WINDOWS & DOORS
Best Practices Guide for Windows & Doors:
CLIMATE, WINDOW CHOICES FOR
CONDENSATION on WINDOWS & SKYLIGHTS
Doors, Exterior, Energy Efficiency Guide
DOOR FLASHING DETAILS
DOORS, ENERGY EFFICIENCY
DOORS, EXTERIOR, Selecting & Installing
GLASS vs HEAT MIRROR SOLAR GAIN/Loss
HURRICANE, WIND, & STORM-Resistant WINDOWS
LOW-E WINDOW GLAZING
LOW-E VS QUAD-GLAZING
LOW-E RETROFIT ADD-ON FILMS
SITE BUILT DOUBLE GLAZED WINDOWS
SLIDING GLIDING WINDOW DEFECTS
SKYLIGHTS, Guide to Choosing & Installing
Skylight Condensation Problems
Skylight Design Issues
Skylight Energy Efficiency
Skylight Installation Procedures
SKYLIGHT LEAK DIAGNOSIS & REPAIR
SKYLIGHT VENTILATION DETAILS
SLIDING GLIDING WINDOW DEFECTS
SLOPED GLAZING DETAILS
SOLAR SHADES & SUNSCREENS
STORM WINDOW INTERIOR
STORM WINDOW PLASTIC CHOICES
STORM WINDOW WEEP HOLES
SUNGAIN, FILMS, LOW-E GLASS
SUNSPACE GLAZING for SUNTANNING
VERTICAL GLAZING DETAILS
VINYL / PVC WINDOW WARPING
WINDOW / DOOR ENERGY EFFICIENT, DOE
WINDOW / DOOR AIR LEAK SEALING HOW TO
WINDOW CERTIFICATION & STANDARDS
WINDOW EFFICIENCY Features & Ratings
WINDOW FLASHING & SEALING Guide
WINDOW GLAZING Based on Climate
WINDOW HARDWARE AGE
Window Installation, Flange-Type
Window Installation, w/ Integral Brickmold
WINDOW LEAKS INTO BASEMENT
Window Materials & Construction
Window Types, Guide
WINDOW TYPES - Photo Guide
Window & Door Sources
WINTERIZE A BUILDING
This article discusses design details for site-built double-glazed windows, including which window pane should be sealed most carefully, venting the space between window panes, the amount of space that should separate window panes, and comparing the cost of factory-built windows with site-built windows.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Our photograph (left) shows an interesting sloped window installation on the roof of a barn silo that had been converted to living space. Conventional wood-frame double-hung windows were set into the sloped silo roof - this was not a successful installation and the windows rapidly rotted, leaked, and disintegrated.
Readers who are building their own windows or who are installing factory-built windows should also see SLOPED GLAZING DETAILS and VERTICAL GLAZING DETAILS. For suggestions about how to diagnose and repair leaks in existing skylights, see SKYLIGHT LEAK DIAGNOSIS & REPAIR.
The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.
Topic: ways to construct site-built double-pane windows
I have heard of various ways to construct site-built, double-pane windows. One way is to seal the inner pane airtight, then to fit the outer window pane somewhat loose. Other ways are similar, involving small holes to let the inner air space "breathe". What do you recommend? Also, what maximum spacing do you recommend between panes of fixed glass in a double-glazed window? - David Lile, Santa Cruz, CA
Since it is virtually impossible to achieve a hermetic seal in site-built windows (except with exotic hot melt window construction systems used sometimes in commercial window retrofits), we agree with your suggestions.
Inner window pane: Keep the inside window pane as airtight as possible to keep moist household air out of the window unit. In sealing window glass it is essential that proper allowances are made for contraction and expansion of materials over the expected temperature range -see THERMAL EXPANSION of MATERIALS.
Outer window pane: provide a moisture escape route to the outdoors once moisture does enter the space between the two window panes. A few 3/8-inch weep holes, drilled through the sill and stuffed with fiberglass or screening (to keep bugs out) is one detail we've seen. This seems preferable to a "loose" outer window pane.
Also see our discussion of storm window weep holes and why they are critical: STORM WINDOW WEEP HOLES
Watch Out for Leaks at Drain Holes Drilled in Wood Window Frames
DJF Note: but beware: drilling through wood window frame components, if they are not properly protected from the weather and from leaks, can lead to serious window frame rot.
Recommended Space Between Window Panes in Double-Glazed Window Construction
As for the recommended spacing distance between panes of glass in a multi-glazed window, beyond 3/4-inch there is no gain in thermal performance. A one-inch double glass window unit is rated at about R-2 versus about R-1.8 for a 5/8-inch spaced window glass unit. [Specific research citations needed here.]
Window glass panes too far apart?
DJF Note: other studies have shown that if the space between window panes becomes too great, even if the window is a factory-sealed unit, thermal convection can cause air movement inside the window, increasing building heat loss during cold weather. For an explanation of convection currents and how they can cause even sealed building cavities to act as heat loss conductors. As we detail at Convective Loops & Thermal Bypass Leaks, stack effects in buildings chill the interior walls - increasing conduction (heat) losses through them. Sealing in the home's interior will reduce infiltration, but it won't stop partitions and plumbing or electrical chases that are open to the attic from filling with cold air. A window whose glass panes are set too far apart can create these same effects, turning a window into a heat pump, sending indoor heat outdoors.
Window glass panes too close together?
DJF Note: other studies have shown that if the space between window panes is too small, even if the window is a factory-sealed unit, radiation losses from the warm inner window surface across the air space between the panes and onto the cold outer window pane will significantly reduce the window's R-value. Stick with the common window pane spacings used by window manufacturers, typically 3/16" to 3/4" between glass panes. [Specific research citations needed here.]
Window Cost Comparison: Site-Built versus Factory Made Double-Pane Windows
Incidentally, in standard window sizes, factory-sealed double-glazed window units cost about the same as two individual lites of glass you would buy to build your own site-built double-glazed windows. So unless you are retrofitting windows of odd sizes, or require extra thick windows, factory-sealed window units may be your best bet.
Our photo (left) shows a skylight that has suffered recurrent leaks at the glazing frame itself.
This unit, patched with tar and roof cement is on a New York college campus and installed in a slate roof where skylight repairs, properly performed, will reduce the frequent need to access this high and fragile slate roof.
For advice on finding and curing the cause of leaks at existing skylights and other sloped glazing, see SKYLIGHT LEAK DIAGNOSIS & REPAIR.
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
The link to the original Q&A article in PDF form immediately below was preceded (above) by an expanded/updated online version of this article.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Questions & answers or comments about do-it-yourself site-built double glazed windows: how to build insulated glass widows and sashes.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References