Building Keene Castle on a Granite Cliff with Nudura® ICF
Project: Keene Castle
Owner/Builder: Lance Keene
Location: White Mountains, New Hampshire
System: Nudura® Insulating Concrete Forms (ICF)
Vision Meets Structural Reality
More than 15 years ago, Lance Keene, a self-taught amateur builder, began building what many considered impossible: a multi-story castle perched 600 feet up on solid granite in the White Mountains of New Hampshire. He was inspired by the German castles he visited while stationed there during his military service in the U.S. Army. Today, the structure stands as a technically ambitious example of ICF construction applied to extreme terrain, severe wind exposure, and complex architectural geometry.
The site is frequently exposed to nor’easters and extreme winds. Mount Washington is only 29 miles away, where the world wind speed record of 231 mph was set in 1934. Wind resilience, thermal performance, and structural redundancy were not optional; they were prerequisites.
From the beginning, Keene selected ICF construction for simplicity, strength and energy efficiency. Keene notes, “ICF seemed like the most logical way to self-build while achieving high R-values and durability.”
To ensure his design could be executed safely, and in compliance with local regulations and energy requirements, all plans were reviewed by a New Hampshire–based structural engineer with expertise in state and local building codes. This review process confirmed that the nontraditional geometry, extensive use of curved walls, and elevated wind-load considerations met applicable New Hampshire code requirements while remaining constructible using ICF systems.
Why Nudura XR35?
Keene initially began with another ICF brand but transitioned to Nudura XR35 after encountering challenges with construction of the turrets. The project includes six turrets with each requiring tight radii and precision block modification.
Keene noted that Nudura’s locking mechanism and block design were superior for his application. Although radius blocks still required back cuts, jigs, and glue-up, the system significantly reduced fabrication complexity compared to hand-cut straight blocks. For ultra-tight spiral stair radii, he developed a special modified saw to fabricate custom radius units.
Product Features
Nudura XR35 8″ core on first floor.
- 4″ of EPS foam on each side
- Factory radius blocks built to specification
Engineering for Wind: Reinforcement Strategy
Given the exposed mountaintop location, structural engineering demanded elevated reinforcement standards.
The typical specification for rebar, per Nudura baseline guidance, is one #4 horizontal rebar per 18″ block. Keene’s engineer had specified #5 horizontal rebar every 12″. Since the Nudura block wasn’t designed for rebar every 12”, Keene opted to use the bottom web too, resulting in an 8”, 10”, 8”, 10” alternating configuration far exceeding the structural engineer’s recommendation. With the vertical rebar, he also changed the 12” recommendation to 8” to accommodate the Nudura block. He intentionally exceeded reinforcement requirements to offset his inexperience as a builder and to address wind loads. The structure is pinned directly to solid granite with #8 rebar epoxied into drilled 18” anchor holes, 9” on center.
Lessons Learned Along the Way
Self-performing a Nudura ICF build is relatively straight forward, but nothing about the Keene castle has been typical or straightforward. The project includes a great deal of customization, combined with a challenging geographic landscape. During the first-floor pour (August 2021), Keene experienced approximately seven blowouts / failures, particularly where curved turrets merged with straight walls at an angle. The subsequent 2nd-floor pour was heavily reinforced with wood bracing at known points of vulnerability, which eliminated blow-outs.
A tactical error, due to inexperience, occurred when switching from 8″ to 6″ blocks on the second floor. While it is not unusual to incorporate blocks with different core sizes to address various structural features within a single building, it requires a seasoned approach to proper alignment of the walls. Without an engineering strategy to transition from the 8” black to the 6” block, the mismatched webs caused alignment challenges and wall lean, requiring additional bracing. This reinforces the importance of maintaining consistent block systems across levels or involving an experienced professional to accommodate the construction variables in core widths when making the transition.
HYDROFOAM Radiant Flooring Integration
To complement ICF wall performance, Keene is incorporating HYDROFOAM® for radiant flooring:
- 4″ HYDROFOAM with 1.5″ concrete topping on primary levels
- 2″ HYDROFOAM on second floor
This assembly supports thermal continuity and aligns with the project’s energy objectives. In a climate with extended freeze cycles, integrating insulated radiant slabs above granite bedrock improves overall system efficiency and reduces long-term energy costs.
Logistics: Building on a Cliff
Material delivery presented significant operational challenges:
- 1,100-foot driveway with 5 steep switchbacks
- Timber for the second floor included Douglas fir from Washington State as large as 32’
- Offloaded in valley, re-trucked in two split loads
- Crane mobilized for upper-level placement
These logistical challenges meant that once snow was on the ground, access was impossible, limiting pour windows and requiring precise seasonal scheduling. In July 2025, wind destroyed gable-end ICF sections one week before a scheduled pour, underscoring the site’s exposure and the need for a comprehensive bracing strategy.
Design Complexity: Turrets, Windows, and Load Paths
The structure includes:
- Six turrets
- A round living room to capture 200-degree mountain views
- Seven windows added in the master suite (exceeding the original plan of only five)
The additional window openings required the installation of lally columns between the narrow vertical wall segments to manage roof load distribution.
Keene rendered the original engineering drawings in Home Designer Pro, which were then converted to AutoCAD by an architect in Brazil, before local engineering review. Structural review emphasized wind load, rebar density, and floor joist spacing.
Phased Construction: Capital and Labor
The project has spanned more than 15 years, which has allowed for phased construction and financing. Keene estimates the eventual valuation of the home at approximately $4 million, with much of the build self-funded. Roof timber installation is scheduled for 2026, requiring a crane.
Performance Drivers for Builders and Designers
- Wind Resilience: High-density rebar, pinned granite footings, and solid concrete cores address extreme mountain exposure.
- Thermal Continuity: XR35 foam layers combined with HYDROFOAM radiant insulation deliver robust R-values suitable for northern climates.
- Acoustic Mass: Although not the primary driver, ICF mass dampens wind noise, which Keene describes as “like a freight train” during storms.
- Geometry Feasibility: Factory radius blocks made complex turret construction viable at scale.
Key Takeaways
- Reinforce heavily at curved-to-straight wall intersections.
- Pre-plan wind bracing beyond code minimum in exposed sites.
- Account for delivery logistics early in mountain or remote builds.
- When designing multiple window penetrations, evaluate concentrated load zones carefully.
The Keene Castle demonstrates how ICF construction, specifically Nudura ICF, can deliver structural resilience, energy performance, and architectural freedom in extreme or unusual environments. For builders and architects evaluating ICF for complex or high-wind sites, this project offers a practical field example of reinforcement strategy, system selection, and real-world problem-solving under complex and unusual conditions.
Completion is targeted for 2028. The structure already stands as a durable, insulated concrete monument to long-term vision, engineered persistence, and the structural advantages of modern ICF systems.
Video Project Documentation
Numerous videos of the construction process are available and can be viewed at the links below:
The castle website: https://www.keenecastle.com/
July 2025: Second-floor concrete pour with drone flyovers (4.5 minutes): https://www.youtube.com/watch?v=SdcvZoCmyps
Sept. 2025: Walkthrough visiting every room (30 minutes): https://www.youtube.com/watch?v=L79W5NnX3tk
July 2025: Wind destroys the gable end ICFs 1 week before our pour: https://www.youtube.com/watch?v=ZW-U1Mer2dM
March 2025, a winter visit and drone flyover: https://www.youtube.com/watch?v=pqEULxIrik4
Sep 2023: Finished 2nd floor deck, the problems with minions: https://www.youtube.com/watch?v=nRfgZPj-nmQ
Placing the timber in 2022: https://www.youtube.com/watch?v=s_AHxEyJnzI
Aug 2021 pouring the first floor walls: https://www.youtube.com/watch?v=wKonJ7xb52o
Aug 2020 first-floor walls start to go up: https://www.youtube.com/watch?v=o0rhZokPjsk
NW Blasting July 2020, the blasting video: https://www.youtube.com/watch?v=a2x6Uu93a6U
2018 Foundation Pour: https://www.youtube.com/watch?v=TO7ssaxQYdQ
2017 Tour of the 2D & 3D drawings (25 mins): https://www.youtube.com/watch?v=fGj3E6EGqKk
2017 footings pour: https://www.youtube.com/watch?v=fRvdUeeoriU
2016: blasting on the cliff for the stairwell turret: https://www.youtube.com/watch?v=l0npbP8WG2Y
2016 Girl Power-Keene’s 5-year-old daughter moving dirt at the castle with the excavator: https://www.youtube.com/watch?v=bt-ssqouwu8
2013: Blasting at the entrance of the driveway: https://www.youtube.com/watch?v=05rusC7uZZY
2008: Keene takes his new wife to the castle site for the first time (translated to English): https://www.youtube.com/watch?v=xXXq8RD4elM
2001: placing the first stones in the terrace: https://www.keenecastle.com/Photo-History/2001/emodule/483/egallery/636