We have a large (too heavy to carry) dog that is a Lab and Greyhound mix. He is 180 or more pounds. We have had him for about 6 years.
He is an outside dog, but is house trained. When the weather is bad, we do let him in and he is perfect. He just sits on the dog rug and won't move unless it's to roll over or get up and stretch. He has never had an accident inside. Perfect behavior.
For years, we have tried to get him to go upstairs (the college girls now live up there on weekends) to sleep in their room. During storms, we have tried to get him to go to the basement with us. He won't do stairs. Never has. He does 3, then stops and sits. He will do the ones on the porches and decks of the house just fine. He just won't inside. The kids even carried him (took 3 of them, when teenagers) upstairs and downstairs to show him it's OK. Once he gets to the spot they carried him to, he is fine. But when its time to do the stairs to go back up or down, he has to be carried again. During the tornado last week, he refused to go down. We had to go down and then he met us at the back basement door to come in (so he knew where the stairs went to in order to meet us at the door).
Any ideas how to get him to do stairs? This momma can't carry him!
From Pets Best: Take small steps until you can lure your dog all the way from the floor to the top step and onto the furniture. Now it is time to teach your dog how to go down the steps.
It seems your dog does not fear 2-4 steps but is afraid to go to higher or lower levels. Have you tried sitting on the 4th or 5th step and encouraging him to try further? No big deal but if he will take even one step and be rewarded and loved he may accept one at a time. From what I have read this may be the only way to help your dog get over his fear of heights.
This type of training will take time and patience but it would be worth it if it helps eliminate his fear.
Be cheery with him, or lure with treats that its okay to use the stairs.